Patent Publication Number: US-2023149632-A1

Title: Auto-injector and related methods of use

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 63/264,121, filed on Nov. 16, 2021, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure is directed to an auto-injector and related methods of use. 
     INTRODUCTION 
     In various available auto-injectors, upon activation by a user, a needle is deployed, and fluid is delivered from the needle into the user. After completion of fluid delivery, the needle may be retracted for user comfort, needle safety, and positive perception of the product. However, many auto-injectors may be inadvertently triggered when dropped or vibrated. Additionally, many auto-injectors may lack suitable control logic for stopping an injection when appropriate. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, the present disclosure is directed to an injection device. The injection device may include: a housing; a container disposed within the housing, the container enclosing a fluid and having a first end and a second end; a conduit movable relative to the container, wherein the conduit is not in fluid communication with the fluid enclosed by the container while in a first position, and is in fluid communication with the fluid enclosed by the container and configured to deliver the fluid from the container to a patient while in a second position; and a lock that is removable from the housing, the lock having a first portion and a second portion. In a first configuration where the lock is coupled to the housing, the first portion of the lock may be disposed exterior of the housing and the second portion of the lock may be disposed within the housing between the container and the conduit; in the first configuration, the conduit may be prevented from moving into fluid communication with the fluid enclosed by the container by the second portion of the lock; and in a second configuration where the lock is removed from the injection device, the conduit may be able to move into fluid communication with the fluid enclosed by the container. 
     In another aspect, the injection device may include: a housing; a plunger coupled to the housing and movable relative to the housing; one or more electronics components used during an injection performed by the injection device, the one or more electronics components being formed within an electrical circuit. In a first configuration, a first portion of the plunger may be disposed within the housing, the electrical circuit may be open, and the one or more electronics components may be in a low-power sleep mode; in a second configuration, the plunger may move outward relative to the housing, and the first portion of the plunger may extend exterior of the housing; and in the second configuration, the electrical circuit may be closed, and the one or more electronics components may be transitioned from the low-power sleep mode, to an active mode. 
     In another aspect, the injection device may include: a housing, wherein the housing includes a curved bottom surface that is concave when viewed from a point external to the housing that is closer to the bottom surface of the housing than a top surface of the housing; a circuit board positioned adjacent to the bottom surface of the housing, wherein the circuit board includes a skin sensor configured to sense a presence of skin in contact with the bottom surface of the housing; and a controller coupled to the circuit board, wherein the controller is configured to initiate an injection by the injection device only after the skin sensor senses the presence of skin in contact with the bottom surface of the housing. 
     In another aspect, the present disclosure is directed to a method of manufacturing an injection device. The method may include: depositing a first material onto a mold, the first material having a first opacity; depositing a second material around the mold and the first material, the second material having a second opacity that is higher than the first opacity; and positioning a container enclosing a medicament within the injection device and adjacent to a first portion of the injection device formed by the first material. 
     In another aspect, the injection device may include: a container disposed within the housing, the container having a first end and a second end; a piston configured to move from the first end of the container toward the second end of the container to dispense a medicament from the container; a drive member configured to drive the piston through the container; an emitter configured to emit a beam of light toward the container; a detector positioned on an opposing side of the container from the emitter, wherein the detector is configured to receive the beam of light emitted from the emitter; and a controller coupled to the drive member, the emitter, and the detector. The controller may be configured to: receive a first signal from the detector while the emitter is off, the first signal corresponding to an ambient level of light surrounding the injection device; receive a second signal from the detector while the emitter is on; calculate a difference between light values represented by the first signal and the second signal; and cease operation of the drive member when the difference is less than a threshold value. 
     In another aspect, the injection device may include: a container disposed within the housing, the container having a first end and a second end; a piston configured to move from the first end of the container toward the second end of the container to dispense a medicament from the container; a drive member configured to drive the piston through the container; an emitter configured to emit a beam of light toward the container; a detector positioned on an opposing side of the container from the emitter, wherein the detector is configured to receive the beam of light emitted from the emitter; and a controller coupled to the drive member, the emitter, and the detector. The controller may be configured to: initiate the drive member and the emitter; receive a first signal from the detector while the emitter is on, the first signal being representative of an amount of light received by the detector; allow for continued operation of the drive member for a first period of time immediately after initiation of the drive member; and cease operation of the drive member upon determining (1) that the amount of light received by the detector is less than a first threshold light value and (2) before the amount of light received by the detector subsequently rises to or above the first threshold light value, that a current of the drive member is greater than a first threshold current value. 
     In another aspect, the injection device may include: a container disposed within the housing, the having a first end and a second end; a piston configured to move from the first end of the container toward the second end of the container to dispense a medicament from the container; a drive member configured to drive the piston through the container; and a controller coupled to the drive member. The controller may be configured to: maintain a speed of the drive member until a current of the drive member exceeds a first threshold; and after the current of the drive member exceeds the first threshold, reduce a voltage of the drive member to maintain the current of the drive member below a second threshold that is greater than or equal to the first threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various examples and together with the description, serve to explain the principles of the disclosed examples and embodiments. 
       Aspects of the disclosure may be implemented in connection with embodiments illustrated in the attached drawings. These drawings show different aspects of the present disclosure and, where appropriate, reference numerals illustrating like structures, components, materials and/or elements in different figures are labeled similarly. It is understood that various combinations of the structures, components, and/or elements, other than those specifically shown, are contemplated and are within the scope of the present disclosure. 
       Moreover, there are many embodiments described and illustrated herein. The present disclosure is neither limited to any single aspect nor embodiment thereof, nor to any combinations and/or permutations of such aspects and/or embodiments. Moreover, each of the aspects of the present disclosure, and/or embodiments thereof, may be employed alone or in combination with one or more of the other aspects of the present disclosure and/or embodiments thereof. For the sake of brevity, certain permutations and combinations are not discussed and/or illustrated separately herein. Notably, an embodiment or implementation described herein as “exemplary” is not to be construed as preferred or advantageous, for example, over other embodiments or implementations; rather, it is intended reflect or indicate the embodiment(s) is/are “example” embodiment(s). 
         FIG.  1    is a perspective view of an auto-injector, according to an example of the disclosure. 
         FIG.  1 A  is a perspective view of a portion of a housing of an auto-injector according to the disclosure. 
         FIG.  1 B  is a perspective view of a portion of a housing of an auto-injector according to the disclosure. 
         FIG.  2    is a bottom view of an auto-injector according to the disclosure. 
         FIG.  3    is a side view of an auto-injector, showing an activating switch extending away from a tissue-facing surface, according to the disclosure. 
         FIG.  3 A  is a cross-sectional view of an auto-injector, showing an activating switch extending away from a tissue-facing surface, according to the disclosure. 
         FIG.  3 B  is a cross-sectional view of an auto-injector, showing an activating switch in a partially depressed position, according to the disclosure. 
         FIG.  3 C  is a cross-sectional view of an auto-injector, showing an activating switch in a fully depressed position, according to the disclosure. 
         FIG.  4    is an exploded view of an auto-injector, according to the disclosure. 
         FIG.  4 A  is a schematic illustration of a control system of an auto-injector according to the disclosure. 
         FIG.  4 B  is an exploded view of an auto-injector according to the disclosure. 
         FIG.  4 C  is a perspective view of a portion of a housing and an electronics board, according to an aspect of the disclosure. 
         FIG.  5    is an exploded view of a needle mechanism according to the disclosure. 
         FIG.  5 A  is a perspective view of a fluid conduit according to the disclosure. 
         FIG.  5 B  is a cross-sectional view of a needle of a fluid conduit according to the disclosure. 
         FIG.  6    is a perspective view of the needle mechanism of  FIG.  5    in a first position according to the disclosure. 
         FIGS.  7 - 11    are side views of the needle mechanism of  FIG.  5   . 
         FIG.  12    is a side cross-sectional view of a portion of an auto-injector according to the disclosure. 
         FIG.  13    is a side cross-sectional view of a piercing mechanism according to the disclosure. 
         FIG.  13 B  is a side cross-sectional view of an auto-injector according to the disclosure. 
         FIG.  14    is a side cross-sectional view of a piercing mechanism according to the disclosure. 
         FIG.  15    is a side view of a needle insert switch according to the disclosure. 
         FIG.  16 A  is a perspective view of a lock for an auto-injector according to an aspect of the disclosure. 
         FIG.  16 B  is a bottom view of an auto-injector and a lock according to the disclosure. 
         FIG.  16 C  is a cross-sectional view of an auto-injector and a lock according to the disclosure. 
         FIG.  16 D  is a cross-sectional view of an auto-injector and a lock according to the disclosure. 
         FIG.  16 E  is a perspective view of a lock for an auto-injector according to an aspect of the disclosure. 
         FIG.  16 F  is a side view of a lock for an auto-injector according to an aspect of the disclosure. 
         FIG.  17    is a bottom view of an electronics board for an auto-injector according to the disclosure. 
         FIG.  17 A  is a perspective view of an electronics board for an auto-injector according to the disclosure. 
         FIGS.  18 - 20    depict flowcharts of exemplary methods according to the disclosure. 
         FIGS.  20 A and  20 B  depict graphs relating to electric controls for an auto-injector according to the disclosure. 
         FIGS.  21 - 23    depict flowcharts of exemplary methods according to the disclosure. 
     
    
    
     Again, there are many embodiments described and illustrated herein. The present disclosure is neither limited to any single aspect nor embodiment thereof, nor to any combinations and/or permutations of such aspects and/or embodiments. Each of the aspects of the present disclosure, and/or embodiments thereof, may be employed alone or in combination with one or more of the other aspects of the present disclosure and/or embodiments thereof. For the sake of brevity, many of those combinations and permutations are not discussed separately herein. 
     Notably, for simplicity and clarity of illustration, certain aspects of the figures depict the general structure and/or manner of construction of the various embodiments. Descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring other features. Elements in the figures are not necessarily drawn to scale; the dimensions of some features may be exaggerated relative to other elements to improve understanding of the example embodiments. For example, one of ordinary skill in the art appreciates that the cross-sectional views are not drawn to scale and should not be viewed as representing proportional relationships between different components. The cross-sectional views are provided to help illustrate the various components of the depicted assembly, and to show their relative positioning to one another. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to examples of the present disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the discussion that follows, relative terms such as “about,” “substantially,” “approximately,” etc. are used to indicate a possible variation of ±10% in a stated numeric value. 
     As described above, existing auto-injectors may be inadvertently triggered when dropped or vibrated. Additionally, existing auto-injectors may lack suitable control logic for stopping an injection when appropriate. These shortcomings may cause premature deployment of drugs, increase complexity of self-administration of drugs, introduce user errors, and cause user discomfort. Accordingly, the present disclosure is directed to various embodiments of an injection device (e.g., auto-injector) for self-administration of drugs, or other therapeutic agents, by a user. Specifically, according to certain embodiments, a likelihood of inadvertent triggering of the auto-injector may be reduced and the auto-injector may further incorporate control logic which improves operation of the auto-injector and user experience. 
     Additional details of auto-injectors in accordance with the present disclosure can be found in PCT/US2018/031077 to Arnott, et al., filed on Nov. 8, 2018, and published as WO 2018/204779 A1, the entirety of which is incorporated by reference herein. Additional details of vial piercing systems in accordance with the present disclosure can be found in U.S. Pat. No. 10,182,969, filed on Mar. 10, 2016, the entirety of which is incorporated by reference herein. 
     Overall System 
     An example of such an auto-injector  2  is shown in  FIGS.  1 ,  2 , and  3   . As shown in  FIG.  1   , auto-injector  2  may include a housing  3  having a tissue-engaging (e.g., bottom) surface  4  through which a needle may be deployed and retracted. As shown in  FIGS.  1  and  1 A , housing  3  may include a transparent window  50 . Transparent window  50  may enable a viewer to visualize one or more displays or to visualize an interior of auto-injector  2  and components therein, such as a primary container and/or a drug product stored in the primary container. 
     In some embodiments, and as shown in  FIG.  1   , auto-injector  2  may include a plurality of openings  51  configured to facilitate the travel of sound generated within housing  3  (by, e.g., a speaker). Auto-injector  2  may have any suitable dimensions to enable portability and self-attachment by a user. In one example, auto-injector  2  may have a length of about 2.98 inches, a width of about 2.07 inches, and a height of about 1.07 inches. However, other suitable values also may be utilized, including, e.g., a length from about 0.5 inches to about 5.0 inches, a width of about 0.5 inches to about 3.0 inches, and a height from 0.5 inches to about 2.0 inches. 
     Auto-injector  2  may be oriented about a longitudinal axis  40  (e.g., an X axis), a lateral axis  42  (e.g., a Y axis) that is substantially perpendicular to longitudinal axis  40 , and a vertical axis  44  (e.g., a Z axis) that is substantially perpendicular to both longitudinal axis  40  and lateral axis  42 . 
     As shown in  FIG.  1   , an adhesive patch  12  may be coupled to tissue-engaging surface  4  to help secure auto-injector  2  to a user&#39;s body (e.g., skin). Adhesive patch  12  may be formed from fabric or any other suitable material, and may include an adhesive. The adhesive may be an aqueous or solvent-based adhesive, or may be a hot melt adhesive, for example. Suitable adhesives also include acrylic based, dextrin based, and urethane based adhesives as well as natural and synthetic elastomers. In some examples, the adhesive provided on patch  12  may be activated upon contact with a user&#39;s skin. In yet another example, patch  12  may include a non-woven polyester substrate and an acrylic or silicone adhesive. Patch  12  may be joined to housing  3  by, e.g., a double-sided adhesive, or by other mechanisms like ultrasonic welding. Patch  12  may have a length dimension greater than a width of auto-injector  2 . 
     As shown in  FIG.  2   , auto-injector  2  may include an opening  6 , through which the needle may be deployed and retracted. An activating switch  1409  may be disposed on tissue-engaging surface  4 , and may be configured to activate auto-injector  2 , or otherwise place auto-injector  2  in a “ready” mode. A touch sensor  1410  also may be disposed on tissue-engaging surface  4 , and may be configured to help a controller of auto-injector  2  determine whether auto-injector  2  is disposed on the skin of a user (indicating that the auto-injector should fire or otherwise deploy a needle), or whether activating switch  1409  was improperly triggered (indicating that operation of auto-injector  2  should be stopped). A connecting port  13  also may be disposed on tissue-engaging surface  4  to facilitate programming of auto-injector  2 . 
     Auto-injector  2  may be configured to operate in three or more operation phases including, e.g., an injection sequence activation phase, an injection phase, and a retraction phase, each of which will be described in further detail herein. The injection sequence activation phase, injection phase, and retraction phase may collectively be referred to herein as an “injection sequence.” 
     Referring to  FIGS.  3 A,  3 B, and  3 C  which show cross-sections of an auto-injector  2 , activating switch  1409  may be a mechanical plunger-type switch. For example, activating switch  1409  may include a plunger  1450  having a plunger contact surface  1452 . Plunger contact surface  1452  may be generally circular in shape (or have another suitable shape) and may be large enough to be depressed comfortably by soft skin. In some embodiments, plunger contact surface  1452  may have a diameter or width ranging from about 2 mm to about 10 mm, a diameter ranging from about 4 mm to about 8 mm, or a diameter of about 6 mm. Activating switch  1409  may further include a shaft  1442 , a biasing member  1444 , a biasing collar  1446 , and a plunger flange  1454 . Biasing member  1444  may be a spring, for example, and may surround shaft  1442 . Biasing member  1444  may be fixed, or otherwise prevented from moving, at one end by biasing collar  1446 . Plunger flange  1454  may be configured to contact or otherwise depress a plunger switch  1448 . For clarity, the term activating switch and/or reference to activating switch  1409 , as used herein, should be understood to encompass any or all components of activating switch  1409 , including shaft  1442 , biasing member  1444 , biasing collar  1446 , plunger switch  1448 , plunger  1450 , plunger contact surface  1452 , and plunger flange  1454 . 
     In a free state, i.e., when plunger  1450  is not depressed, either by being pressed against the skin of a user or otherwise, plunger  1450  may extend outwardly from tissue-engaging surface  4  as shown in  FIG.  3 A . In the free state, plunger contact surface  1452  may be a distance from tissue-engaging surface  4  ranging from about 1 mm to about 16 mm, ranging from about 5 mm to about 12 mm, or a distance of about 8.5 mm. In the free state, biasing member  1444  may urge plunger  1450  to extend outwardly from tissue-engaging surface by pressing against biasing collar  1446 . In the free state, plunger flange  1454  may be in contact with, or otherwise depress plunger switch  1448 . When plunger flange  1454  is in contact with, or otherwise depresses plunger switch  1448 , an electrical circuit associated with plunger switch  1448  may be complete, or closed. 
     When plunger  1450  is depressed either by being pressed against the skin of a user or otherwise, plunger  1450  may initially move to a partially depressed state, as shown in  FIG.  3 B . In the partially depressed state, biasing member  1444  may be compressed against biasing collar  1446 . Plunger flange  1454  may further be out of contact with, or otherwise not depressing plunger switch  1448 . When plunger flange  1454  is spaced apart from, not in contact with, or is otherwise not depressing plunger switch  1448 , the electrical circuit associated with plunger switch  1448  may be broken, or open. By this configuration, the auto-injector  2  may be maintained in a reduced power state while plunger  1450  is depressed, such as when auto-injector  2  is in packaging. 
     As shown in  FIG.  3 B , plunger  1450  may not necessarily travel to the fully depressed state (shown in  FIG.  3 C ) before plunger flange  1454  is out of contact with plunger switch  1448 . As shown in  FIG.  3 C , on the other hand, in the fully depressed state, plunger  1450  may be depressed inwardly such that plunger contact surface  1452  is flush or nearly flush with tissue-engaging surface  4 . 
     Plunger flange  1454  may be out of contact with plunger switch  1448 , for example, after less than 5 mm of travel by plunger  1450 , after less than 3 mm of travel by plunger  1450 , after less than 1 mm of travel by plunger  1450 , or after about 0.75 mm of travel by plunger  1450 —all when, for example, the maximum depression distance is 8.5 mm. In other words, plunger  1450  may transition from the free state, in which plunger flange  1454  is in contact with plunger switch  1448 , to the partially depressed state, in which plunger flange  1454  is out of contact with plunger switch  1448 , after moving only a portion of a maximum depression distance of plunger  1450  relative to housing  3  of auto-injector  2 . For example, plunger  1450  may transition to the depressed state after moving only about 5%, about 10%, or about 20% of the maximum depression distance. Accordingly, the auto-injector  2  and plunger switch  1448  may be sufficiently responsive upon depressing plunger  1450  against a user&#39;s skin. For example, auto-injector  2  and plunger switch  1448  may be sufficiently responsive when pressed against skin of varying firmness or users having varying body fat content. While examples of travel distances for plunger  1450  are provided herein, it is to be understood that the present disclosure is not limited to any particular examples and any suitable travel distance may be used. 
     Biasing member  1444  may be sufficiently stiff such that in the free state, plunger flange  1454  stays in contact with or otherwise continuously depresses plunger switch  1448 . Biasing member  1444  may also be of a stiffness such that plunger  1450  may be depressed comfortably when pressed against a user&#39;s skin. Biasing member  1444  may be biased to maintain plunger  1450  in the free state. 
     Though activating switch  1409  is shown in  FIGS.  3 A- 3 C  as a mechanical plunger-type switch, it is to be understood that activating switch  1409  may be any other suitable type of switch, such as a rocker switch, throw switch, toggle switch, temperature switch, and the like. Additionally, while the electrical circuit associated with plunger switch  1448  is described herein as closed when plunger  1450  is in the free state and open when plunger  1450  is in the depressed state, it should be understood that an opposite configuration may be used. For example, the electrical circuit associated with plunger switch  1448  may be open when plunger  1450  is in the free state and closed when plunger  1450  is in the depressed state. 
     A method of controlling auto-injector  2  according to positions of activating switch  1409  will be described hereinafter in further detail with reference to  FIG.  23   . 
     Further, as shown in  FIG.  4 B , in some embodiments, auto-injector  2  may include a plurality of LEDs  52 . The LEDs  52  may be arranged in a ring-like formation, or any other suitable formation. As described in further detail hereinafter, light from the one or more LEDs  52  may be indicative of various operational states of the auto-injector  2 . 
     Auto-Injector Housing 
     Referring to  FIGS.  1 A and  1 B , the housing  3  of auto-injector  2  may include an upper portion  30 . The upper portion  30  may form a portion of the housing  3  opposite tissue-engaging surface  4 . The upper portion  30  may include transparent window  50  through which a user may be able to see contents of the auto-injector  2 , including a vial and/or a drug contained in the vial. The transparent window  50  may be positioned on a side of the upper portion  30  and may be formed such that it conforms to a rounded/curved contour of the upper portion  30 , as shown in  FIG.  1   . The transparent window  50  may be generally rectangular in shape with rounded corners. 
     The upper portion  30  may also include a plurality of transparent windows  54 . The transparent windows  54  may be formed on a top surface of upper portion  30  and may be arranged in any suitable configuration, such as a circular configuration, an oval configuration, a rectangular configuration, or a linear configuration, for example. Transparent windows  54  may be circumferentially spaced apart from one another, for example. The transparent windows  54  may allow light from one or more LEDs located within the housing  3  to be visible to a user. The light from the one or more LEDs may be indicative of various operational states of the auto-injector  2 , as described herein. 
     The transparent window  50  and the transparent windows  54  may be integrally formed as part of the upper portion  30 . As shown in  FIG.  1 B , the upper portion  30  may include a transparent portion  500  formed from a transparent material. The transparent portion  500  may be contiguous, such that the transparent window  50  and the transparent windows  54  are formed of one piece of transparent material. Moreover, the transparent portion  500  may be integrated into the upper portion  30  such that the upper portion  30 , including the transparent window  50  and the transparent windows  54  is manufactured as a single part. 
     To form the upper portion  30  as a single part, the upper portion  30  may be manufactured using a double shot molding process, for example.  FIG.  19    illustrates an exemplary method  1900  of molding the upper portion  30  using double shot molding or insert molding. At step  1910 , a first material may be deposited into a first mold having a first core and a first mold cavity. The first material may have a low opacity and may be, for example, a transparent material for the transparent window  50  and the transparent windows  54 . The first material may be, for example, transparent acrylic, clarified acrylonitrile butadiene styrene (ABS), polycarbonate, polyvinylchloride (PVC), or polyethylene terephthalate glycol (PETG). The first mold may be configured, for example, to form transparent portion  500 . 
     At step  1920 , the first core and the material in the first mold cavity, may be moved within a second mold cavity to form a second mold. When moved, the first core may retain the first material. The second mold may be configured, for example, to form the upper portion  30 . At step  1930 , a second material may be deposited into the second mold cavity in which the first material is contained. The second material may be deposited around the first material and first core in unoccupied space of the second mold cavity to form the upper portion  30 . The second material may be a material with high opacity, such as white plastic. The second material may be, for example, ABS, polycarbonate, ABS-polycarbonate blend, PVC, or PETG. 
     Accordingly, the generally opaque upper portion  30 , which includes the transparent window  50  and the transparent windows  54  may be formed from two different materials to form a single part. Forming the upper portion  30  as a single part may reduce an overall number of steps required to assemble auto-injector  2 . For example, in some embodiments, no fastening or adhesive steps or materials are needed to join transparent and opaque portions of the housing. Avoiding unnecessary assembly steps may further improve the appearance of cosmetic surfaces of the auto-injector  2 . Additionally, forming the upper portion  30  as a single part may improve the overall structural integrity of the auto-injector  2 . Further, forming the upper portion  30  as a single part may reduce or eliminate sinks on cosmetic surfaces. 
     Needle Mechanism 
     Referring to  FIGS.  5 - 11   , a needle mechanism  20  includes a carrier  202  that is movable (e.g., slidable) within housing  3  between a first position ( FIG.  6   ) and a second position ( FIG.  7   ). Needle mechanism  20  also may include a fluid conduit  300  that is mounted to carrier  202 , and which may be deployed into a user, and retracted by a driver  320 . A shuttle  340  (e.g., a shuttle actuator) may be configured to move driver  320  via a deployment gear  360 , and a retraction gear  362 . Shuttle  340  may be coupled to a resilient member (e.g., a spring  370 ). A cover  380  ( FIG.  5   ) may be coupled to carrier  202  to enclose various components of needle mechanism  20 . 
     Referring to  FIG.  5   , fluid conduit  300  may extend from a first end  302  to a second end  304 . As shown in further detail in  FIG.  5 A , first end  302  may include a needle  306  that is configured to be injected into a user. Needle  306  may include a sharp and/or beveled tip, and may extend generally along or parallel to axis  44 . Second end  304  may include a needle  308  that is substantially similar to needle  306 , but may be positioned within auto-injector  2  to penetrate a cartridge  1302  (shown in  FIG.  13    and described in further detail below) to access drugs to be injected into the user. Fluid conduit  300  may include an intermediate section  310  including one portion extending along or parallel to axis  40 , and a second portion extending along or parallel to axis  40 . The first and second portions of intermediate section  310  may be joined in a serpentine section  312  that facilitates flexion of fluid conduit  300  and movement of needle  306  along axis  44  during deployment into the user, and during retraction out of the user. While a serpentine section  312  is shown, any other suitable shape, e.g., a coil, curved, or other shape that enables flexion of fluid conduit  300  is also contemplated. Serpentine section  312 , or similar structure, may act as a cantilever when needle  306  is deployed and/or retracted. Serpentine section  312  also may bias fluid conduit  300  into the deployed configuration shown in  FIG.  5   . Once needle  308  penetrates and establishes fluid communication with cartridge  1302  (see, e.g.,  FIG.  14   ), drugs may travel from cartridge  1302 , through needle  308 , intermediate section  310 , and needle  306  (pierced through the user&#39;s skin), and into the user. In some examples, fluid conduit  300  may include only metal or a metal alloy. In other examples, fluid conduit  300  may be any other suitable material, such as, e.g., polymers or the like. Needle  308  and intermediate portion  310  may define a 22 or 23 Gauge, thin-walled needle, while needle  306  may be a 27 Gauge, thin-walled needle. Other needle sizes ranging from, e.g., 6 Gauge to 34 Gauge, and other needle wall thicknesses, such as regular wall, extra-thin wall, and ultra-thin wall also may be utilized as appropriate. Fluid conduit  300  may reduce the amount of material that contacts the drugs, reduce joints and assembly steps, and require less sterilization than conventional devices. 
     As shown in  FIG.  5 B , needle  308  may be configured to include a needle tip  308   a  and a side port  308   b . Side port  308   b  may be fluidly connected to fluid path  308   c  and allow fluid to enter fluid conduit  300  through a side of needle  308 , as opposed to through the tip of needle  308 . A rear wall of side port  308   b  may be inclined at an angle θ relative to a longitudinal axis of fluid path  308   c . In some embodiments, the angle θ may be between about 20° and 60°, between about 30° and 50°, or about 40°. By configuring needle  308  in this way, needle  308  may be optimized for piercing the primary container of auto-injector  2 , which may be a sealed cartridge or a vial. The relative positioning of needle tip  308   a  and side port  308   b  may allow piercing of the seal of the primary container without coring or otherwise cutting a portion of the seal with an opening to fluid path  308   c . Thereby, entry of particles cored or cut from the seal into the fluid path  308   c  may be minimized or avoided. 
     Needle  306  may be configured substantially similarly to needle  308 , as shown in  FIG.  5 B . Alternatively, in some embodiments, either or both of needles  306  and  308  may be a 3 bevel needle, a 5 bevel needle, or any other suitable type of needle. In some embodiments, one or both of needles  306  and  308  may be a pencil point needle having a round hole or any other suitably shaped hole. 
     Carrier  202  may be formed of plastic (e.g., injection-molded plastic), a metal, metal alloy, or the like, and may include a flange  204  with an opening  206 , and posts  210  and  212 . Carrier  202  also may include an opening  216  through which a needle or other fluid conduit may be deployed. Opening  216  may be a slot that is recessed from an end surface of carrier  202 , or, in an alternative embodiment, an entirety of the perimeter of opening  216  may be defined by material of carrier  202 . Carrier  202  also includes a driver path  218 . Driver path  218  may be a slot in carrier  202  that extends along or parallel to axis  44 . Driver path  218  may be configured to receive a protrusion of driver  320 , such as, e.g., protrusion  330  discussed in further detail below. Carrier  202  also may include a shuttle path  220 , along which shuttle  340  may move, as described in further detail below. 
     Carrier  202  also may include a stop  240  that is configured to engage shuttle  340 . Stop  240  may be a cantilever having a fixed end  241  ( FIG.  8   ) and a free end  242  ( FIG.  8   ). Stop  240  may include an inclined ramp  243  ( FIGS.  9  and  12   ) that, when engaged or pushed by a ramp  1500  (described with reference to  FIG.  12   ), causes stop  240  to deflect about fixed end  241 . In a first position, free end  242  may block or otherwise impede movement of shuttle  340 , and in a second configuration, may permit movement of shuttle  340 . The relationship between stop  240  and shuttle  340  will be discussed in further detail later in the application. 
     Driver  320  includes two racks  322  and  324  (shown in  FIG.  8   ) parallel to one another and disposed on opposing sides of driver  320 . Racks  322  and  324  may include teeth and may be configured to engage with and drive rotation of deployment gear  360  and retraction gear  362 , respectively. Driver  320  may include a lumen  326  (or a track, recess, or other suitable structure) ( FIG.  5   ) that is configured to receive needle  306  of fluid conduit  300 . Driver  320  also may include protrusion  330  ( FIGS.  6  and  7   ) that is configured to slide within driver path  218  of carrier  202 . Protrusion  330  may include a hook-like configuration that can “catch” on impediment  600 , as described in further detail below. 
     With continuing reference to  FIG.  5   , shuttle  340  may include a rack  342  configured to engage with gears  360  and  362 . Shuttle  340  also may include an end surface  344 , and a recess  346  that extends along a length of shuttle  340  in the same direction as rack  342 . A slot  348  ( FIG.  9   ) may extend along the length of recess  346 . Slot  348  may extend through the middle of recess  346  and may extend along an entirety or substantial entirety of recess  346 . 
     Shuttle  340  may move along track  220  from a first, starting position ( FIG.  8   ), to a second, intermediate position ( FIGS.  9  and  10   ), and from the second position to a third, final position (shown between the second and third configurations in  FIG.  11   ). As shuttle  340  moves along track  220 , rack  342  may first engage deployment gear  360 , and then retraction gear  362 . At certain times, rack  342  engages at most one of deployment gear  360  and retraction gear  362  at any given time. In some examples, such as when rack  342  is disposed longitudinally between deployment gear  360  and retraction gear  362 , rack  342  is not engaged with either of deployment gear  360  and retraction gear  362 . Shuttle  340  may be configured to move only along one axis (e.g., axis  40 ) and only in one direction along the one axis. The force required to move shuttle  340  along track  220  may be provided by expansion of spring  370 . Spring  370  may be compressed from a resting state, and the expansion of spring  370  may move shuttle  340  along track  220  through the series of positions/configurations set forth above. At various positions of shuttle  340 , different features of auto-injector  2  may directly or indirectly block movement of shuttle  340 . Alternatively, it is contemplated that spring  370  may be biased to a compressed configuration. In this alternative embodiment, spring  370  may be expanded from a resting state, and compression of spring  370  may move shuttle  340  along track  220  through the series of positions/configurations set forth above. 
     The first position of shuttle  340 , shown in  FIG.  8   , may correspond to an unused, undeployed, and/or new state of auto-injector  2 . In this first position, driver  320  may be in an undeployed state. Shuttle  340  is maintained in the first position by the positioning of an impediment  600  in the path of driver  320  ( FIG.  6   ). Impediment  600 , which may be a shelf of housing  3 , or another suitable blocking device, may prevent movement of driver  320  by engaging and/or retaining protrusion  330 . Therefore, because driver  320 , deployment gear  360 , and rack  342  are coupled to one another, the blockage of driver  320  also prevents movement of shuttle  340 . Shuttle  340  may move from the first position to the second position by moving impediment  600  relative to carrier  202  (or vice versa). In one example, carrier  202  is moved (e.g., to the left in  FIG.  6   ) while impediment  600  remains stationary. 
     When the path of driver  320  is free from impediment  600  ( FIG.  7   ), spring  370  may expand and move shuttle  340  along track  220 . This linear movement of shuttle  340  may rotate deployment gear  360  counter-clockwise (or clockwise in other examples) via rack  342 , and the rotation of deployment gear  360  may move driver  320  downward along axis  44 , via rack  322  of driver  320 . This downward movement of driver  320  may cause needle  306  to pierce through the skin of a user. In some examples, driver  320  may be configured to move, relative to carrier  202 , along only axis  44 . 
     Shuttle  340  may be moved by the expansion of spring  370  until its end surface  344  abuts free end  242  of stop  240  such that shuttle  340  is maintained in the second position shown in  FIGS.  9  and  10   . At this point, free end  242  may prevent further expansion of spring  370  and further movement of shuttle  340  along track  220 . In this second position, fluid conduit  300  may be deployed within a user, and fluid from cartridge  1302  may be injected into the user via needle  306 . Additionally, while shuttle  340  is in the second position, rack  342  may be engaged with deployment gear  360  to maintain needle  306  in the deployed configuration. Shuttle  340  may move from the second position to the third position by the flexion of stop  240  about its fixed end  241 . Further details of this flexion are set forth below with respect to  FIGS.  12 - 14   . The flexion of stop  240  may allow spring  370  to continue expanding, urging shuttle  340  further along track  220 . In some examples, stop  240  may be received by and/or within recess  346  of shuttle  340 , and ramp  243  may slide within slot  348 , as shuttle  340  moves from the second position to the third position. 
     The movement of shuttle  340  from the second position to the third position may correspond to the retraction of needle  306  from the user into housing  3 . In particular, rack  342  may engage with and rotate retraction gear  362  in the same direction (e.g., counter-clockwise or clockwise) as deployment gear  360  was rotated. The rotation of retraction gear  362  may urge driver  320  back to a retracted position via rack  324 . Shuttle  340  may reach the third position, where driver  320  is fully-retracted, when its end surface  344  engages a wall of carrier  202 , when free end  242  of stop  240  reaches an end of recess  346 , and/or when spring  370  reaches a resting state. 
     In some embodiments, once driver  320  moves from the deployed state back to the retracted state, it may be prevented from moving out of the retracted state. As a result, needle  306  will be prevented from re-deployment into the user. In this configuration, auto-injector  2  may be a single-use device (e.g., discarded after completing one injection). In other embodiments, auto-injector  2  may be reset and reused. Furthermore, deployment gear  360  and retraction gear  362  may be the only rotating gears disposed within auto-injector  2 , in some examples. 
     Piercing System and Sterile Connector 
       FIGS.  13  and  14    show features of a piercing system  1300  of auto-injector  2 . Additional details of exemplary piercing systems can be found in U.S. Patent Application Publication No. 2016/0262984 A1 to Arnott et al., published on Sep. 15, 2016, the entirety of which is incorporated by reference herein. Piercing system  1300  includes a primary container, which may be a cartridge  1302  with a first end  1304  and a second end  1306 . The primary container may alternatively be a chamber, syringe, vial, flexible sac, or any other suitable fluid containing structure. 
     Cartridge  1302  may include a cavity  1308  opened at first end  1304  and extending toward second end  1306 . Second end  1306  may include a neck  1310  with a cap  1312  that engages neck  1310  to close second end  1306 . A septum  1314  may be positioned between cartridge  1302  and cap  1312  to assist with closing second end  1306 , and allow for needle  308  (e.g., a staked needle) to be inserted into cartridge  1302 . Cavity  1308  may be closed at first end  1304  by a piston  1316 . 
     Cartridge  1302  may have a 5 mL capacity in some examples, although any other suitable volume (e.g., from 1 mL to 50 mL, or from 2 mL to 10 mL, or from 3 mL to 6 mL, or from 2 mL to 5 mL, or another suitable range) also may be utilized depending on the drug to be delivered. In other examples, cartridge  1302  may have a capacity greater than or equal to 1 mL, or greater than or equal to 2 mL, or greater than or equal to 3 mL, or greater than or equal to 4 mL, or greater than or equal to 5 mL, or greater than or equal to 10 mL, or greater than or equal to 15 mL. Cartridge  1302  may contain and preserve a drug for injection into a user, and may help maintain sterility of the drug. Cartridge  1302  may have a 13 mm diameter neck, a 45 mm length, and an internal diameter of 19.05 mm. These values are merely exemplary, and other suitable dimensions may be utilized as appropriate. In some examples, cartridge  1302  may be formed using conventional materials, and may be shorter than existing devices, which can help auto-injector  2  remain cost-effective and small. Cartridge  1302  may be a shortened ISO 10 mL cartridge. 
     Septum  1314  may include an uncoated bromobutyl material, or another suitable material. Piston  1316  may include a fluoropolymer coated bromobutyl material, and also may include a conical nose  1316   a  to help reduce dead volume within cartridge  1302 . Piston  1316  may include one or more rubber materials such as, e.g., halobutyls (e.g., bromobutyl, chlorobutyl, florobutyl) and/or nitriles, among other materials. 
     Piercing system  1300  also may include a top  1354  positioned at second end  1306 . Top  1354  may include a base  1355  positioned over septum  1314  and the opening of cartridge  1302 . Top  1354  may include a chamber  1356  extending from base  1355  in a direction away from piston  1316 . Chamber  1356  defines a cavity  1357  and includes an opening  1358  in communication with cavity  1357 . In some embodiments, top  1354  may be integrated with septum  1314  (e.g., integral or of one-piece construction). In alternative embodiments (not shown), top  1354  may be provided or initially assembled on fluid conduit  300  and not installed directly on/with cartridge  1302  and/or integrated with septum  1314 . 
     A portion of fluid conduit  300 , such as needle  308 , a tube or the like, may extend through opening  1358  of chamber  1356  and into cavity  1357 , but not through base  1355  in the pre-activated state. Opening  1358  may be pre-formed, or may be formed by the penetration of needle  308  through chamber  1356 . Opening  1358  of chamber  1356  may form a sterile sliding seal about needle  308  such that pathogens or other contaminants are prevented from passing into cavity  1357 . Needle  308  can move relative to top  1354  without disrupting the sterile seal therebetween. Cavity  1357  may be sterile or aseptic such that the inner surfaces of cavity  1357  and needle  308  are sterile. In another embodiment, cavity  1357  may be sterilized after needle  308  is inserted through opening  1358  and into cavity  1357 . In alternative embodiments, rather than top  1354 , a convoluted flexible (e.g., rubber) bellows or bladder member may form cavity  1357  and allow translation of cartridge  1302  relative to needle  308  (or vice versa). The flexible member also may seal or form cavity  1354  about needle  308  after sterilization. 
     Piston  1316  may be coupled to a translation mechanism  1366  that is configured to translate piston  1316  and cartridge  1302  in a direction toward second end  1306 . The movement of piston  1316  toward second end  1306  causes piston  1316  to act against the contents within cartridge  1302  (e.g., drugs, medications), which ultimately transfers force against second end  1306  of cartridge  1302 , causing cartridge  1302  to move along longitudinal axis  40 . Translation mechanism  1366  may include a 12 mm motor with a five-stage gear reduction (360:1). Translation mechanism  1366  may have spring contacts that create an electrical connection with an associated printed circuit board (e.g., first electronic board  1402 ). The motor may be configured to generate a torque of about 136 mN*m at 36 rpm. These design parameters of the motor are merely exemplary, and any other suitable motor also may be utilized. 
     Translation mechanism  1366  may include a leadscrew mechanism coupled to piston  1316  that extends axially upon relative rotation about longitudinal axis  40 . This telescoping leadscrew may have a 100 N output, a 20 mm stroke, and a 7°/45° buttress thread shape with a 0.75 mm pitch. The materials for the leadscrew mechanism may include acetal and polybutylene terephthalate. The leadscrew mechanism may extend within piston  1316  to reduce dead space behind piston  1316 . While piston  1316  is shown in  FIGS.  13  and  14    with longitudinally spaced threads, in some examples, such threads may not be present. In another exemplary embodiment (not shown), translation mechanism  1366  may include a manually engageable surface or member that is manually manipulated by a user to move piston  1316 . For example, piercing system  1300  may include a cartridge or a plunger coupled to the back side of piston  1316 . In another exemplary embodiment (not shown), translation mechanism  1366  may include a pneumatic or hydraulic drive member that is actuated or initiated by a user to move piston  1316 . The drive member may be in the form of expanding bellows, an expanding bladder, an expanding diaphragm, or a sliding seal or piston, for example. The direct pneumatic or hydraulic pressure may provide the force required to move piston  1316 . 
     Piercing system  1300  also includes a collar  1390  coupled or fixed to second end  1306 . Collar  1390  may include a plurality of circumferentially spaced apart fingers  1392  that engage and surround neck  1310 . Collar  1390  may be fixed, or otherwise coupled to second end  1306 . Collar  1390  may include a wall  1390   a  that extends at least partially about neck  1310 , the opening of second end  1306 , cap  1312 , septum  1314 , and/or top  1354 . Wall  1390   a  of collar  1390  may be positioned radially or laterally outward of neck  1310  and extend longitudinally past neck  1310 , cap  1312 , and septum  1314 . 
     In the pre-activated state of piercing system  1300  shown in  FIG.  13   , an edge  1393  of collar  1390  may engage a corresponding radially or laterally inwardly extending cam, latch or actuation portion  1394  of a driver retainer member  1395 . Retainer member  1395  may be slidable relative to collar  1390 . Collar  1390  and retainer member  1395  may be configured such that in the pre-activated state or arrangement shown in  FIG.  13   , at least a portion of the cam or actuation portion  1394  of retainer member  1395  is positioned directly behind a retaining portion  1399  of a driver  1398  slidable within retainer member  1395 . A wall  1391  of driver  1398  may extend into and through an end cap portion  1396  of retainer member  1395  and into an interior portion of retainer member  1395 , and retaining portion  1399  of driver  1398  may extend radially outward from wall  1391 . In some embodiments, wall  1391  of driver  1398  may be substantially cylindrical and retaining portion  1399  of driver  1398  may be a flange extending about an end of the wall  1391 . 
     In the pre-activated state of piercing system  1300 , an elastically deformed biasing or resilient member  1397  may be positioned between cap portion  1396  of retainer member  1395  and retaining portion  1399  of driver  1398 . Biasing member  1397  may exert a force against driver  1398  in the pre-activated state of piercing system  1300  acting in the direction towards cartridge  1302 . Biasing member  1397  may be any member effective in applying the force in the pre-activated state, and then releasing such force upon activation, as discussed below with reference to  FIG.  14   . In some embodiments, biasing member  1397  may be a conical or flat spring. 
     Needle  308  of fluid conduit  300  may be fixed or coupled to driver  1398  such that fluid conduit  300  moves with driver  1398 . In the pre-activated state of piercing system  1300 , needle  308  may be positioned within the sterile cavity  1357 , but not through base  1355  of top  1354 , septum  1314 , and/or into cavity  1308  of cartridge  1302 . 
     In some embodiments, in lieu of cavity  1357 , needle  308  may be positioned within a plug when the piercing system  1300  is the pre-activated state. The plug may be a solid plug which is devoid of any holes, cavities, or openings, and which may be formed of a first rubber material. The first rubber material may be permeable to a sterilizing gas, such as, e.g., ethylene oxide or vaporized hydrogen peroxide. The first rubber material may include one or more of isoprene, ethylene propylene diene monomer (M-class) rubber (EPDM), and styrene-butadiene, among others. The permeability of the first rubber material to a sterilizing gas may allow needle  308 , when disposed within the plug, to be sterilized before use. The plug may be molded about needle  308 , so that needle  308  is impaled into the plug. 
     To move piercing system  1300  from the pre-activated state of  FIG.  13   , translation mechanism  1366  may be activated to move piston  1316  towards second end  1306  and translate cartridge  1302  along longitudinal axis  40  toward driver  1398 . Because the needle  308  is not yet in fluid communication with cartridge  1302 , activation of translation mechanism  1366  applies a pressure against the fluid contained in cartridge  1302 , which is then applied to cartridge  1302  itself. This pressure also causes edge  1393  to push against and deflect actuation portion  1394  radially outward. Without actuation portion  1394  blocking its path, retaining portion  1399  and needle  308  are moved toward cartridge  1302  by the expansion of biasing member  1397 . Driver  1398  may be coupled to flange  204  of carrier  202 , and thus, this movement of driver  1398  toward cartridge  1302  also may move carrier  202  in the same direction. This movement corresponds to the movement of carrier  202  relative to housing  3  in  FIGS.  6  and  7   , which enables protrusion  330  to clear impediment  600  to inject needle  306 . 
     The movement of needle  308  toward second end  1306  of cartridge  1302  also causes needle  308  to pierce through base  1355  of top  1354 , septum  1314 , and cavity  1308 , into fluid communication with the contents of cartridge  1302 . Once needle  308  is in fluid communication with cartridge  1302 , further movement of piston  1316  toward second end  1306  urges fluid through needle  308  and a remainder of fluid conduit  300 . In some embodiments, piercing system  1300  may be configured such that, after activation, no more of needle  308  than the portion that was already positioned within sterile cavity  1357  extends into cavity  1308 . This may help prevent contamination of the contents of cartridge  1302  with non-sterile portions of needle  308 . 
     Biasing member  1397  may be configured to expand such that fluid conduit  300  pierces top  1354  and/or septum  1314  at a high speed, such as at a speed of at least about 10 mm/sec, or at least about 40 mm/sec. The relatively quick piercing of top  1354  and/or septum  1314  via biasing member  1397  may help prevent leakage of the contents of cavity  1308  which may be under pressure via piston  1316 . 
     After drugs have been delivered to the user via needle  306 , needle  306  may be automatically withdrawn from the user. Referring to  FIGS.  12 - 14   , translation mechanism  1366  may be operated in a reverse mode such that the rotation of the lead screw is in an opposite direction compared to the insertion step. This counter-rotation may cause piston  316  to move back toward first end  1304 , and also cause cartridge  1302  to move in an opposite direction along axis  40  (as compared to during fluid delivery and insertion of needle  306 ). The movement of cartridge  1302  in the opposing direction may cause ramp  1500  in  FIG.  12    (which is attached to wall  1391 ) to push against ramp  243  of stop  240 . This may cause stop  240  to deflect about its fixed end  241  in the direction of arrow  240   a , and allow shuttle  340  to move from its second position to its third position to retract needle  306  as set forth above. In this way, withdrawal and insertion of the needle into a patient can both be accomplished with a single spring within the device. 
     It is further contemplated that fluid conduit  300  may be the only fluid conduit of auto-injector  2  configured to be in fluid communication with cartridge  1302 . Thus, drugs from cartridge  1302  may be deployed only through fluid conduit  300  and into the user during normal operation of auto-injector  2 . Additionally, needle  306  may be the only needle of auto-injector  2  configured to be deployed into a patient. In this way, a single piece of metal or plastic can be used to carry the fluid from cartridge  1302  to a patient. 
     Locking Component (Drop Pin) 
     Referring to  FIGS.  16 A- 16 D , auto-injector  2  may include a locking component  1610 . As shown in  FIG.  16 A , locking component  1610  may include a lock (e.g., a protrusion)  1612  having a curved surface  1614  and may further include a cover portion  1616 . Cover portion  1616  may be shaped to conform to tissue-engaging surface  4  of auto-injector  2 , as shown in  FIG.  16 D . Cover portion  1616  and tissue-engaging surface  4  may be concave to receive an anatomical portion  1600  of a user. Anatomical portion  1600  may be, for example, a thigh, hip, arm, posterior, or any other area of the body suitable for injection. Lock  1612  may be connected to cover portion  1616 . In some embodiments, locking component  1610  may be formed as a single piece, such that lock  1612  and cover portion  1616  are integrally connected. Locking component  1610  may be formed from any suitable rigid or semi-rigid material. Locking component  1610  may, for example, be formed of acrylonitrile butadiene styrene (ABS) and may further have a frosted clear appearance indicating that locking component  1610  is disposable. 
     As shown in  FIGS.  16 B- 16 C , locking component  1610  may be disposed on or adjacent tissue-engaging surface  4  of the auto-injector  2  such that lock  1612  may extend into auto-injector  2 . Locking component  1610  may further be disposed on or adjacent a liner  12   a  which may initially cover adhesive patch  12  prior to use of auto-injector  2 . Locking component  1610  may be positioned relative to liner  12   a  such that upon removal of liner  12   a  from adhesive patch  12 , locking component  1610  may also be removed from tissue-engaging surface  4 . Lock  1612  may extend into auto-injector  2  via lock opening  1630  formed in tissue-engaging surface  4 . When locking component  1610  is disposed on or adjacent tissue-engaging surface  4 , cover portion  1616  may be attached to tissue-engaging surface  4  via an adhesive disposed between cover portion  1616  and tissue-engaging surface  4 . Locking component  1610  may be disposed on or adjacent tissue-engaging surface  4  such that it is selectively removable by a user. 
     Referring to  FIGS.  16 C-D , when locking component  1610  is disposed on or adjacent tissue-engaging surface  4 , lock  1612  may extend into auto-injector  2  such that it prevents movement of one or more internal mechanisms of auto-injector  2 . For example, when locking component  1610  is disposed on or adjacent auto-injector  2 , lock  1612  may extend into auto-injector  2  such that lock  1612  engages with one or more internal components of auto-injector  2 , preventing those components from moving and/or being activated. 
     Referring to  FIG.  16 D , when locking component  1610  is disposed on or adjacent tissue-engaging surface  4 , lock  1612  may extend into auto-injector  2  such that it is disposed within piercing system  1300 . As described herein previously, collar  1390  may be coupled or fixed to second end  1306  of cartridge  1302 . As also described herein previously, when piercing system  1300  is moved from the pre-activated state, cartridge  1302  and consequently collar  1390  may translate in a direction parallel to a longitudinal axis of cartridge  1302  toward retaining portion  1399 . When lock  1612  extends into auto-injector  2  and is adjacent to collar  1390 , lock  1612  may prevent cartridge  1302  from translating toward retaining portion  1399  or otherwise prevent cartridge  1302  and collar  1390  from applying a force against actuation portion  1394 . Thus, even if the motor were somehow activated while lock  1612  is disposed in its locking position, fluid communication between needle  308  and cartridge  1302  could not be established and needle  306  could not be deployed outside of housing  3 . Furthermore, when in the locking position, lock  1612  may prevent the movement of cartridge  1302  toward needle  308 , thereby preventing deflection of actuation portion  1394  and consequently preventing retaining portion  1399  and needle  308  from moving toward cartridge  1302 . In the event of auto-injector  2  being dropped or being subject to vibrations, lock  1612  may further prevent piercing system  1300  from being moved from the pre-activated state and consequently may prevent cartridge  1302  from being pierced by the needle  308 . 
     When locking component  1610  is disposed on or adjacent tissue-engaging surface  4 , locking component  1610  may additionally serve as a spacer between a user&#39;s skin and tissue-engaging surface  4 . For example, locking component  1610  may have a thickness such that touch sensor  1410 , described in greater detail hereinafter, is unable to detect the user&#39;s skin thereby avoiding inadvertent activation of auto-injector  2 . Locking component  1610  may have a thickness, for example, from about 1 mm and about 5 mm, or about 3 mm. 
     Accordingly, locking component  1610  may act as an effective safety mechanism to prevent inadvertent activation of auto-injector  2 . When locking component  1610  is disposed on or adjacent the tissue-engaging surface  4 , lock  1612  may prevent various internal components of auto-injector  2  from moving. In the event auto-injector  2  is dropped on the floor prior to use, for example, locking component  1610  may prevent inadvertent piercing of cartridge  1302  and/or inadvertent initiation of an injection sequence. Locking component  1610  may also prevent such movement and/or inadvertent initiation of an injection sequence should auto-injector  2  be subjected to vibration during transport. 
     If a user wishes to use and/or is ready to use auto-injector  2 , the user may separate locking component  1610  from tissue-engaging surface  4 , thereby removing lock  1612  from lock opening  1630 . The user may, for example, peel cover portion  1616  off of tissue-engaging surface  4 . Alternatively, the user may peel liner  12   a  away from adhesive patch  12 , thereby removing locking component  1610  from tissue-engaging surface  4 . When separating locking component  1610  from tissue-engaging surface  4 , curved surface  1614  may allow lock  1612  to rock within lock opening  1630 , thereby allowing lock  1612  to be easily removed from lock opening  1630 . With lock  1612  removed from lock opening  1630 , auto-injector  2  may be in a state in which it is ready to be used such that, e.g., an injection sequence may be initiated. 
       FIGS.  16 E and  16 F  depict locking component  1610  according to some embodiments. As shown in  FIGS.  16 E and  16 F , locking component  1610  may have an increased width (relative to the depiction of locking component  1610  in  FIGS.  16 A- 16 C ) to ensure locking component  1610  extends over touch sensor  1410  when locking component  1610  is disposed on auto-injector  2 . Moreover, locking component  1610  may have a ribbed structure and may include air gaps or recesses  1618  and hinges  1620 . Air gaps  1618  may inhibit conduction of a capacitive field between the user&#39;s skin and touch sensor  1410  when the auto-injector  2  is placed near the user with locking component  1610  in place. Hinges  1620  may allow locking component  1610  to flex when locking component  1610  is peeled from auto-injector  2 . In some embodiments, a removable cover other than and/or separate from locking component  1610  may extend over touch sensor  1410  to inhibit inadvertent skin detection. 
     Electronics 
       FIG.  4 A  shows a control system  1400  of auto-injector  2 . Control system  1400  may include components positioned on a first electronics board  1402  and a second electronics board  1404 , and also may include a power source  1406 . First electronics board  1402  may include a controller  1408 , an activating switch  1409 , a touch sensor  1410 , a needle insert switch  1412 , and an emitter  1414 . Second electronics board  1404  may include a detector  1416 , an audio module  1418 , a visual module  1420 , and a haptic module  1422 . Though  FIG.  4 A  depicts audio module  1418 , visual module  1420 , and haptic module  1422  as included in second electronics board  1404 , in some embodiments, one or more of the foregoing modules may be included on the first electronics board  1402  One or more of the components of first electronics board  1402  and second electronics board  1404  may be operatively coupled to controller  1408 , and powered by power source  1406 . Controller  1408  also may be operatively coupled to translation mechanism  1366 , and may be configured to control operation of translation mechanism  1366  to initiate and control needle insertion and retraction as set forth above. Translation mechanism  1366  may be coupled to first electronics board  1402  via one or more spring contacts during a final assembly step where cartridge  1302  is inserted into housing  3 . As described herein previously, translation mechanism  1366  may include a motor, gearing, and a leadscrew mechanism. 
     The majority of the assembly of auto-injector  2  may occur, e.g., on an assembly line at a manufacturing facility. Then, two device halves (or portions) may be shipped to a drug filling or final assembly facility. Indeed, the two separate portions  1490  and  1492  need not be the same size, as illustrated in  FIG.  4 B . Once a drug vial, e.g., cartridge  1302 , is filled with a drug or other medicament, cartridge  1302  may be assembled with a remainder of auto-injector  2 . For example, the two device halves (portions  1490  and  1492 ) may be assembled together with the filled drug cartridge  1302  therein. In one example, portion  1490  and translation mechanism  1366  may be snapped in place behind cartridge  1302 . Portion  1490  may be part of housing  3  including a base or module configured to contain translation mechanism  1366  and its associated electronics. Portion  1492  may be a part of housing  3  containing substantially all of the other components described herein, including, e.g., the needle mechanism, sterile connector, and piercing mechanisms described herein. In this example, an electrical connection of the motor of translation mechanism  1366  must be made during the snapping of translation mechanism  1366  behind cartridge  1302  (i.e., during the assembly step where portions  1490  and  1492 , and cartridge  1302  are combined to form a complete and functional auto-injector  2 ). To accommodate such an electrical connection, the drivetrain of translation mechanism  1366  may include one or more spring contacts  1494  (referring to  FIG.  4 C ) that will contact pads  1495  (also referring to  FIG.  4 C ) on the first electronics board  1402  upon assembly. Though not depicted in  FIG.  4 C , the drivetrain of translation mechanism  1366  may include additional spring contacts that may contact additional pads on the first electronic board  1402  upon assembly. Such additional spring contacts and additional pads may serve to connect additional components of the translation mechanism  1366 , such as a tachometer, a motor encoder, or any other sensors or devices, to the first electronics board  1402 . Thus, the connection of translation mechanism  1366  to first electronics board  1402  (including controller  1408 ) may be made without any loose wires or other similar structures. 
     Such an assembly process may be relatively simpler than simpler devices (e.g., auto-injectors) with relatively more complex final assembly processes. As a result, the contemplated assembly process described herein may lead to a reduction of labor costs. 
     In some embodiments, auto-injector  2  may include a single (i.e., only or exactly one) electronics board  1710  as shown in  FIGS.  17  and  17 A , on which the components of control system  1400  described herein previously may be positioned. As shown in  FIG.  17 A , electronics board  1710  may include a first board segment  1712  and a second board segment  1714 . The first board segment  1712  and the second board segment  1714  may be physically and electrically connected via a flexible segment  1716 . Flexible segment  1716  may be, for example, a ribbon cable, a flexible conductive substrate, or the like. In some embodiments, flexible segment  1716  may be formed of fiberglass board that is machined thinly enough to flex, and is sometimes referred to as “semi-flex.” In some embodiments, flexible segment  1716  may be formed of a flexible polymer. The flexible polymer may be formed by a process sometimes referred to as “rigid-flex” in which a sandwich of a first portion fiberglass, flexible polymer, and second portion of fiberglass is first formed. The first and second portions of fiberglass may be subsequently removed to leave the thin flexible polymer portion. 
     Electronics board  1710  may include one or more brackets  1720  for mounting or otherwise securing electronics board  1710  to an interior of auto-injector  2 . The first board segment  1712  may further include a cutout  1718 . The cutout  1718  may be positioned such that first board segment  1712  may be positioned to allow the needle to pass through cutout  1718  when deployed. 
     In some embodiments, first board segment  1712  may correspond to first electronics board  1402  and second board segment  1714  may similarly correspond to second electronics board  1404 , each as described herein previously. By connecting first board segment  1712  and second board segment  1714  via flexible segment  1716 , first board segment  1712  may be positioned adjacent to tissue-engaging surface  4  of the auto-injector  2  whereas second board segment  1714  may be positioned on an opposite side of auto-injector  2  toward upper portion  30  of housing  3 . Accordingly, the single electronics board  1710  may be utilized to both connect components located toward tissue-engaging surface  4  and connect components located toward upper portion  30 . Such a configuration may allow for ease of assembly of the auto-injector  2  by obviating a need for complex wiring or soldering. 
     As shown in  FIG.  17   , electronics board  1710  may be positioned within housing  3 . First board segment  1712  may be positioned adjacent to tissue-engaging surface  4  whereas second board segment  1714  may be positioned on an opposite side of auto-injector  2  (e.g. behind first board segment  1712  in  FIG.  17   ). Flexible segment  1716  may be flexed or folded to maintain a connection between first board segment  1712  and second board segment  1714  in such positions. 
     Touch sensor  1410  may be incorporated in or on first board segment  1712  of electronics board  1710 . To allow for adequate detection of a user&#39;s skin, touch sensor  1410  and first board segment  1712  may be located close to tissue-engaging surface  4  of housing  3 . Tissue-engaging surface  4  of housing  3 , or a portion thereof adjacent to touch sensor  1410 , may be sufficiently thin such that an electric field of detectable magnitude may form between touch sensor  1410  and a user&#39;s skin. In some embodiments, the portion of tissue-engaging surface  4  adjacent touch sensor  1410  may be less than about 2 mm, about 1 mm, or less than about 1 mm. Further, the portion of tissue-engaging surface  4  adjacent touch sensor  1410  may be made from a solid material, such as plastic. By forming the portion of tissue-engaging surface  4  adjacent touch sensor  1410  from a solid material, as opposed to a ribbed, cored, or hollow material, a dielectric constant between the user&#39;s skin and touch sensor  1410  may optimize a responsiveness of touch sensor  1410 . 
     Additionally, touch sensor  1410  may be positioned in or on electronics board  1710  so as to be adjacent to or near opening  6  through which the needle may be deployed. By positioning touch sensor  1410  adjacent to or near opening  6 , a likelihood that touch sensor  1410  may detect a user&#39;s skin when auto-injector is positioned appropriately is increased. Furthermore, a curvature of tissue-engaging surface  4  may decrease the likelihood that touch sensor  1410  may falsely interpret a flat surface such as a tabletop to be a user&#39;s skin by creating a space between touch sensor  1410  and the flat surface. 
     By incorporating touch sensor  1410  in or on electronics board  1710 , a need for one or more wires and/or other circuitry connecting touch sensor  1410  to a separate electronics board may be eliminated. Assembly of the auto-injector  2  may thereby be simplified and a cost of the auto-injector may be reduced. 
     As electronics board  1710  may be located adjacent to tissue-engaging surface  4 , electronics board  1710  may include a cutout to allow the needle to be deployed through electronics board  1710  and subsequently through opening  6 . Further, electronics board  1710  may be positioned such that touch sensor  1410  is directly adjacent opening  6  and no gap exists between an edge of touch sensor  1410  and opening  6 . Alternatively, electronics board  1710  may be positioned such that a gap exists between an edge of touch sensor  1410  and opening  6  and the gap has a maximum of width of 5 mm, 2 mm, or 1 mm, for example. 
     Controller  1408  may be configured to accept information from the system and system components described above, and process the information according to various algorithms to produce control signals for controlling internal mechanisms of auto-injector  2 , including translation mechanism  1366 . Examples of such algorithms are described hereinafter with reference to  FIGS.  18  and  20 - 23   . The processor may accept information from the system and system components, process the information according to various algorithms, and produce information signals that may be directed to audio module  1418 , visual module  1420 , haptic module  1422 , or other indicators of, e.g., second electronics board  1404 , in order to inform a user of the system status, component status, procedure status or any other useful information that is being monitored by the system. The processor may be a digital IC processor, analog processor or any other suitable logic or control system that carries out the control algorithms. 
     As discussed above with respect to  FIGS.  3 A and  3 B , activating switch  1409  may be a mechanical plunger-type switch that extends away from tissue-engaging surface  4  of auto-injector  2 . Activating switch  1409  may include an electrical circuit that is complete unless activating switch  1409  is depressed. For example, when auto-injector  2  is attached to a user&#39;s skin, switch  1409  may be depressed, breaking the electrical circuit, and indicating to controller  1408  that auto-injector  2  should be activated. In order to conserve power, the components of auto-injector  2  may be in an idle or sleep mode until switch  1409  is activated. In yet another example, auto-injector  2  may not be powered at all until switch  1409  is activated, and deactivation of switch  1409  may cut off power to auto-injector  2  entirely. While a mechanical plunger-type switch is disclosed, any other suitable mechanism for activating auto-injector  2  may be utilized, including, e.g., a button depressed by the user, voice signals, and a wireless signal from another electronic device, among others. 
     Touch sensor  1410  may be configured to help controller  1408  determine whether auto-injector  2  is properly deployed on the skin of a user. In one example, touch sensor  1410  may be a capacitive sensing electrode or any other device configured to differentiate contact with skin versus other materials, such as, e.g., wood, plastic, metal, or another material. When skin is in the proximity of the capacitive sensing electrode, a signal indicative of such contact may be sent to controller  1408 . Thus, touch sensor  1410  may serve to verify that auto-injector  2  is properly placed on a user&#39;s skin, even if switch  1409  is depressed. Touch sensor  1410  may include a capacitive sensing electrode coupled to first electronics board  1402  and also to an interior of housing  3 . Housing  3  and adhesive patch  12  may act as an overlay (insulator) that acts as a dielectric between the skin of the user and the capacitive sensing electrode. Alternatively, touch sensor  1410  may be incorporated in or on electronics board  1710 , as described herein previously, such that the capacitive sensing electrode is also incorporated in or on electronics board  1710 , Contact of portions of housing  3  and/or adhesive patch  12  near the capacitive sensing electrode may cause the capacitance of the electrode to increase, for example, by about 1 to about 10 pF, indicating placement of auto-injector  2  on a skin surface. 
     Needle insert switch  1412  may be configured to send a signal to controller  1408  that needle  306  is deployed within a user. For example, referring to  FIG.  15   , needle insert switch  1412  may include a curved cantilever  1510  including a first contact  1512 . Needle insert switch  1412  also may include a second contact  1514 . First contact  1512  may be placed into electrical contact with second contact  1514  when needle  306  is deployed into the user. During deployment of needle  306 , driver  320  may move downward along axis  44  and deflect curved cantilever  1510  and first contact  1512  toward second contact  1514 . When first contact  1512  and second contact  1514  connect to one another, a signal may be sent to controller  1408  indicating that needle  306  has been successfully deployed into the user. The separation of first contact  1512  and second contact  1514  may indicate that needle  306  has been retracted from the user. 
     Emitter  1414  and detector  1416  may operate as an optical interruption sensor, or photo-interrupter in order to allow controller  1408  to determine a state of auto-injector  2 . Emitter  1414  may be a light emitting diode (LED) or other suitable light emitter, and detector  1416  may be, e.g., a phototransistor configured to receive light emitted by emitter  1414 . In one example, emitter  1414  may emit infrared light, although other suitable wavelengths of light also may be used. The use of infrared light may help reduce interference from external light. 
     As shown in  FIG.  13 B , emitter  1414  and detector  1416  may be arranged across from one another within housing  3  to enable a beam of light  1430  to pass from emitter  1414 , through cartridge  1302 , to detector  1416 . Cartridge  1302 , and any fluid contained therein may be at least partially transparent to beam  1430  so that beam  1430  may pass through cartridge  1302  and its contents. As piston  1316  is moved toward second end  1306  during drug delivery (referring to  FIGS.  13  and  14   ), piston  1316 , and in particular a shoulder of piston  1316 , may interrupt beam  1430 . When detector  1416  fails to sense beam  1430 , a signal may be sent to controller  1408 , which may interpret the signal to indicate an end of an injection (e.g., that all of the drug contained within cartridge  1302  has been expelled). In some examples, the refraction path of beam  1430  may be considered when positioning emitter  1414  and detector  1416  relative to one another. For example, beam  1430  may be refracted as it passes through cartridge  1302  and any liquid contained therein, and emitter  1414  and detector  1416  may be offset from one another accordingly. Additionally, emitter  1414  and detector  1416  may be offset from a center of housing  3  so that the shoulder of piston  1316  may block beam  1430 . In at least some examples, an optical interruption sensor or similar mechanism may help avoid false positives in the event of a drive train failure. That is, the optical switch may help controller  1408  determine that an injection was not completed with greater accuracy than other mechanisms. 
     Audio module  1418  may include a speaker or the like to provide audio feedback to the user. Openings in housing  3  may facilitate the travel of sound from audio module  1418  to the user. Audio module  1418  may generate a tone or other sound at the start and at the end of injection, and/or to indicate any other benchmark during the injection, such as an error, for example. Visual module  1420  may include one or more LEDs or similar devices to provide visual feedback to the user. Visual module  1420  may include different colored LEDs to provide various messages to the user. For example, a plurality of blue LEDs arranged in a ring could be used to display progress of the injection over time, one or more green LEDs could be used to display completion of the injection, and a red LED could be used to display an error to the user. Any other suitable colors, combinations, and/or numbers of LEDs may be used in various examples. For example, a combination of red, blue, and purple LEDs may be utilized. In one arrangement, eight LEDs may be arranged in a circle having a diameter of about 26.5 mm, or a diameter from about 10.0 mm to about 40.0 mm. It is to be understood that this exemplary quantity and positioning of LEDs is not intended to be limiting and any quantity and/or positioning of LEDs may be used. The LEDs may be activated sequentially around the circle to indicate progress of an injection (e.g., in a progress ring arranged in a similar manner as a clock—see, for example, LEDs  52  on  FIG.  4 B ). Controller  1408  also may be configured to receive feedback from various sensors, and rescale a speed that various LEDs are activated based on feedback from the sensors. For example, the LEDs in the progress ring may be activated in three or more operation phases including, e.g., an injection sequence activation phase, an injection phase, and a retraction phase. Those of ordinary skill in the art will recognize that auto-injector  2  may have more or less than the above-described three operation phases. There may be an expected time for completing each phase, but there also may be some variability in the actual times experienced during any of the aforementioned operation phases of auto-injector  2 . An algorithm may be utilized to help avoid the premature activation of LEDs, for example, when a certain phase finishes earlier than expected, or to have progress along the ring stopped when a certain phase takes longer than expected. At any given point, the algorithm may divide the remaining estimated time for completion of drug delivery by the number of unactivated LEDs in the progress ring, to determine a rate at which the remaining LEDs in the progress ring should be activated. 
     For example, before the injection sequence activation phase, the LEDs may be activated at a rate equal to the estimated time of the entire drug delivery process (e.g., the estimated time to complete all of injection sequence activation phase, the injection phase, and the retraction phase) divided by the total number of unactivated LEDs in the progress ring. Stated differently, the estimated time of the entire drug delivery process may be divided by a number that is the total number of LEDs in the progress ring less any already-activated LEDs. Thus, if, for example, one LED is already activated, the estimated time of the entire drug delivery process may be divided by one less than the total number of LEDs in the progress ring. 
     After completion of the injection sequence activation phase, the LEDs may be activated at a rate equal to the sum of estimated times for completing the remaining phases (e.g., the injection phase and the retraction phase) divided by the number of unlit LEDs in the progress ring. After completion of the injection phase, the LEDs may be activated at a rate equal to the estimated time to complete the retraction phase, divided by the number of unlit LEDs. 
     In some embodiments, subsets of LEDs may be used to indicate progress of injection phases. For example, in embodiments having eight LEDs positioned on a housing of auto-injector  2 , a first LED may be illuminated to indicate needle insertion. The second through seventh LEDs may then be illuminated sequentially to indicate a progress of the injection phase. Lastly, the eighth LED may be illuminated to indicate needle retraction. While an exemplary configuration of the LEDs and corresponding logic has been described, it should be understood that the quantities of LEDs for each phase of an injection process may be varied as desired. 
     Visual module  1420  also may include a display screen, touch screen, or other suitable device to provide one-way or two-way communication with the user. Visual module  1420  may be visible by the user from outside of housing  3  via a window in housing  3 . Haptic module  1422  may include, e.g., a haptic motor configured to generate vibrations that can be felt by the user. Vibrations may signal the start and the end of an injection, and/or may help provide additional information to a user. 
     Controller  1408  may be coupled to a wireless communication module and an antenna. The wireless communication module may be configured to transmit data from controller  1408  to, e.g., a mobile device, computer, cell phone, or the like. The wireless communication module may be configured to transmit information over one or more wireless modalities, such as, e.g., Bluetooth, Bluetooth low energy (BLE), near-field communication (NFC), infrared, cellular networks, and wireless networks, among others. The antenna may be any suitable device configured to assist the wireless communication module in data transmission and/or amplification. Thus, controller  1408  may be configured to transmit diagnostic information of the user and/or auto-injector  2 , information pertaining to completion of an injection, and/or information pertaining to an error state of auto-injector  2  to a device of the user, or to the cloud. Signals indicative of needle insertion and/or early device removal also could be transmitted via the wireless communication module. Controller  1408  may also be configured to transmit temperature information for auto-injector  2 . For example, a user may be able to monitor, via a mobile device and/or application, for example, a temperature of auto-injector  2  when auto-injector  2  is removed from refrigeration. Controller  1408  also may receive activation and/or delay commands via the wireless communication module. Controller  1408  may further receive operation adjustment commands such as commands relating to adjustment of preferred operation speed, for example. In some embodiments, controller  1408  may receive a command to pause an injection. 
     In some embodiments, controller  1408  may communicate with a mobile application of a user&#39;s mobile device via the wireless communication module. The mobile application may be configured to facilitate use of auto-injector  2  and improve user experience. In some embodiments, the mobile application may be used to automatically check an expiration date of a medicament contained within auto-injector  2 . Such functionality may relieve a user from having to manually check the expiration date and may improve user safety. Based on an expiration date, the mobile device may be configured to alert the user and/or disable use of the auto-injector  2 . In some embodiments, the mobile application may be used to alert a user as to product recalls and/or may disable the device in the event of product recalls. For example, the mobile application may access a database via the internet to determine whether particular devices, lots of devices, medicaments, and/or lots of medicaments have been recalled. In some embodiments, the mobile application may be configured to confirm whether the auto-injector  2  and/or medicament is authentic as opposed to counterfeit. The mobile application may do so by, for example, cross-referencing a product serial number or a digital signature against a database of authenticated products. In some embodiments, a portion or portions of auto-injector  2  may be disposable and the mobile application may be configured to confirm the authenticity of such portion or portions prior to use. 
     In some embodiments, the mobile application may be used to facilitate an injection sequence. For example, the mobile application may sync with the events of an injection sequence and provide contemporaneous instructions to the user as to which tasks (e.g., depress switch  1409 , hold auto-injector  2  against skin, remove auto-injector) to perform at which times. In some embodiments, the instructions may be narrated audibly. In some embodiments, the instructions may be provided visually via a display on the mobile device. In some embodiments, the mobile application may be configured to provide a detailed indication of a progress of an injection sequence. For example, the mobile application may provide text, visual, and/or audible indications of progress with greater granularity than shown by LEDs, for example, as described herein previously. 
     In some embodiments, the mobile application may be configured to record and store a date and/or time of an injection. Based on the date and/or time of the injection, and a user&#39;s prescription information, the mobile application may be configured to automatically create a reminder for a subsequent injection. In some embodiments, upon completion of an injection, the mobile application may be configured to provide a notification to the user with positive feedback for adherence to a prescription regimen. In some embodiments, the mobile application may provide points and/or rewards for continued adherence. 
     In some embodiments, the mobile application may be configured to authenticate a user of the auto-injector  2  prior to use. For example, the mobile application, in connection with the user&#39;s mobile device, may use biometric identification, two-factor authentication, or any other suitable authentication protocol to confirm the identity of the user prior to an injection. Upon authentication of the user, the mobile application may cause the auto-injector to become activated or otherwise be unlocked. Such user authentication may inhibit misuse and/or waste of costly medicaments by persons other than an intended user. 
     In some embodiments, the mobile application may be configured to detect operating conditions of auto-injector  2 . For example, the mobile application may be configured to detect a battery level of the device and in case of a low battery indication, the mobile application may be configured to provide a notification to the user indicative of a need to charge the device. In some embodiments, the mobile application may be configured to detect mechanical and/or electrical malfunctions of auto-injector  2  and convey such information to the user. 
       FIG.  18    shows an exemplary method  2000  according to the disclosure. Method  2000  may start at step  2002 , where a user may position auto-injector  2  on her body so that tissue-engaging surface  4  contacts a skin surface. The user may position auto-injector  2  on her skin after removing locking component  1610 , as described herein previously, thereby allowing touch sensor  1410  to detect proximity of the skin. Auto-injector  2  may be mounted in any suitable location, such as, e.g., the thigh, abdomen, shoulder, forearm, upper arm, leg, buttocks, or another suitable location. Auto-injector  2  may be secured to the skin by adhesive patch  12 . The securement of auto-injector  2  at step  2002  may cause activating switch  1409 , which extends outward from tissue-engaging surface  4 , to be depressed and break a circuit. The breaking of the circuit may cause a signal to be sent to controller  1408  indicative that activating switch  1409  has been depressed. Alternatively, any other suitable mechanism may power on or otherwise activate auto-injector  2  before or after step  2002 . Upon depression of activating switch  1409 , auto-injector  2  may emit an audio tone and/or illuminate one or more LEDs (e.g., one or more LEDs of a first color, e.g., blue) to indicate depression of activating switch  1409 . 
     Once auto-injector  2  is activated at step  2002 , method  2000  may proceed to step  2004 , where controller  1408  may determine whether tissue-engaging surface  4  is positioned on a skin surface. At step  2004 , controller  1408  may receive a measurement from touch sensor  1410  indicating whether auto-injector  2  is positioned on skin or another surface. If controller  1408  determines that touch sensor  1410  is in contact with skin, for example, when a capacitance value received from touch sensor  1410  is within a predetermined range, method  2000  may proceed to step  2008 . If controller  1408  determines that touch sensor is not in contact with skin, for example, if the capacitance measurement received from touch sensor  1410  indicates that auto-injector  2  is in contact with a non-skin surface like wood or metal, method  2000  may proceed to step  2006 . At step  2006 , auto-injector  2  may be placed into an error condition. In the error condition, an LED may be activated (e.g., a red LED) to indicate to the user that an error has occurred, or a message may be displayed on a display screen. In some examples, auto-injector  2  may need to be manually reset before an injection can be completed. In other examples, auto-injector  2  may loop back to step  2004 , wherein controller  1408  continuously attempts to determine whether touch sensor  1410  is in contact with skin. Method  2000  also may require that touch sensor  1410  be in contact with skin during the entire injection. Thus, if at any point during the injection, controller  1408  determines that touch sensor  1410  is no longer in contact with skin, controller  1408  may stop the injection (e.g., by stopping further movement of translation mechanism  1366 ), may generate an error signal or message, and may retract needle  306  if it had been extended. By stopping the injection and retracting needle  306 , a risk of dispensing the drug outside of the body (i.e. a wet injection) and/or needle stick injuries may be mitigated. Upon the determination of step  2004 , auto-injector  2  may emit an audio tone and/or illuminate one or more LEDs to indicate that the auto-injector  2  is positioned on the skin surface. In one example, one or more additional LEDs of the first color may be illuminated at this stage to indicate further progress of the injection. 
     At step  2008 , controller  1408  may send a signal to activate translation mechanism  1366 . Once activated, translation mechanism  1366  may move toward second end  1306  of cartridge  1302  (referring to  FIGS.  13  and  14   ), causing cartridge  1302  itself to move in the same direction. This may cause needle  308  to move in the opposing direction to access cartridge  1302  as set forth above. The movement of driver  1398  and needle  308  causes carrier  202  to move in the same direction, which sets forth the chain of events that ultimately deploys needle  306  into the user by the mechanisms set forth in  FIGS.  5 - 11   . Translation mechanism  1366  will continue to move toward second end  1306  until a desired amount of the drug contained within cartridge  1302  is dispensed into the user. Upon activation of the translation mechanism, auto-injector  2  may emit an audio tone and/or illuminate one or more LEDs to indicate that the injection is in progress. For example, yet additional LEDs of the first color may be illuminated as the injection progresses to give the user a visual indication of the progression. 
     Method  2000  may proceed to step  2010 , where controller  1408  may determine whether the injection is complete. This determination may be based on interruption of beam  1430  by piston  1316  (as described with reference to  FIGS.  4 A,  13 , and  14   ). That is, when beam  1430  is broken (not received by detector  1416 ), controller  1408  may determine that injection is complete. Once controller  1408  determines that the injection is complete, controller  1408  may send a signal to translation mechanism  1366  to reverse the direction of rotation of the lead screw, which may cause ramp  1500  to push against ramp  243  of stop  240 , enabling retraction of needle  306  as discussed above with reference to  FIG.  11   . In one example, controller  1408  may institute a delay after receiving an indication that beam  1430  has been interrupted. The delay may be from, e.g., 0.1 to 60 seconds. 
     An additional end detection mechanism may be used instead of or in combination with the interruption-type sensor described above. For example, a current of the motor of translation mechanism  1366  may be utilized to determine whether an injection has been completed. That is, when piston  1316  reaches second end  1306  of cartridge  1302 , the current on the motor will increase (e.g., as a result of piston  1316  engaging the end of cartridge  1302 ), signaling the expulsion of all or substantially all of the contents of cartridge  1302 . One exemplary combination could include the use of beam  1430 , where interruption of beam  1430  indicates that, e.g., 90 to 98 percent of the injection has been completed. Then, the current of the motor of translation mechanism  1366  could be analyzed to determine whether the remaining 2 to 10 percent of the injection has been completed. In another example, instead of using an optical switch, a delay from the initiation of the translation mechanism  1366  may be used by controller  1408  to determine when to reverse translation mechanism  1366 . In one example, this delay may be from, e.g., about 1 to about 120 seconds, although other suitable times are also contemplated. In any event, the delay from initiation may be long enough to permit emptying of cartridge  1302 . In still another example, beam  1430  may be used in combination with an encoder. The encoder may be configured to detect a position of piston  1316 . If the encoder were used to detect the position of piston  1316  alone, a drive train issue could inhibit accurate detection. For example, piston  1316  may rotate when pushed by the lead screw. Such rotation may cause uncertainty as to actual position of piston  1316 . When used in conjunction with beam  1430 , however, controller  1408  may be configured to recalibrate the encoder in response to interruption of beam  1430 . Such recalibration may allow controller  1408  to update the actual position of the encoder and resume accurate detection of the position of piston  1316  using the encoder. 
     Upon determination that the injection is complete, auto-injector  2  may emit an audio tone and/or illuminate one or more LEDs to indicate completion of the injection. In some examples, one or more LEDs of a second color (e.g., green) that is different from the first color may be illuminated to signal to the user that the injection is complete. In some examples, all of the LEDs of the device may be illuminated with the second color, and other indications also may be used. For example, all of the LEDs may be illuminated with the second color and may flash intermittently at the end of the injection. 
     In some examples, a timing of an injection procedure, measured from the initial activation of activating switch  1409  to retraction of needle  306  from the user after drug delivery, may be from about 20 seconds to about 90 seconds, or from about 25 seconds to about 60 seconds, from about 30 seconds to about 45 seconds, or less than or equal to about 120 seconds, or less than or equal to about 90 seconds, or less than or equal to about 60 seconds, or less than or equal to about 45 seconds, or less than or equal to about 30 seconds. Such timing represents a significant improvement over existing devices, for which the timing of an injection may be much longer and, in some cases, as long as about 9 minutes or even longer. 
     Method  2000  also may include additional steps. For example, method  2000  may include determining whether a drug within cartridge  1302  is too cold for delivery into the user, whether power source  1406  has enough energy to complete an injection, whether needle  306  has been prematurely deployed and/or retracted, whether the current of the motor of translation mechanism  1366  is in an appropriate range, and whether an injection procedure has extended beyond a maximum acceptable procedure time. When controller  1408  senses any of the above errors, it may communicate such errors to the user, and may end an ongoing injection by, e.g., halting or reversing translation mechanism  1366  and retracting needle  306  from the user. Auto-injector  2  may emit an audio tone and/or illuminate one or more LEDs indicative of any of the foregoing additional steps. For example, one or more LEDs of a third color (e.g., red) that is different than the first and second colors may be illuminated. 
       FIG.  20    shows an exemplary method  2020  of controlling a torque of the motor of translation mechanism  1366  and detecting when the motor stalls. At step  2022 , controller  1408  may initiate an injection sequence. As described herein previously, an injection sequence may be initiated upon depressing activating switch  1409  against a user&#39;s skin and/or detecting the user&#39;s skin by touch sensor  1410 . During the injection sequence, a voltage may be applied to the motor of translation mechanism  1366  to drive the motor. 
     At step  2024 , as the injection sequence progresses, controller  1408  may maintain the motor of translation mechanism  1366  at a constant speed. The constant speed may be, for example, a rotational speed measured in revolutions per minute (RPM). Controller  1408  may maintain the motor at a constant speed by varying the voltage applied to the motor. For example, when a higher load is applied to the motor due to an obstruction, increased fluid pressure, increased component friction, or any other cause, controller  1408  may compensate for the increased load by increasing the voltage applied to the motor. Conversely, when a load applied to the motor is reduced, controller  1408  may compensate for the reduction in load by decreasing the voltage applied to the motor. Maintaining the motor at a constant speed may reduce a likelihood that the user experiences injection site pain. For example, maintaining the motor at a constant speed may prevent the bolus from become excessively large, thereby mitigating the risk of pain. 
     During the injection sequence, controller  1408  may monitor a current supplied to the motor. The motor current may be indicative of a torque generated by the motor. For example, a higher motor current may indicate a higher torque being generated by the motor. At step  2026 , controller  1408  may determine whether the motor current exceeds a first current threshold. The first current threshold may be determined and/or set based on a maximum torque that may be safely generated by the motor. The maximum torque may be reached, for example, when the injection sequence is obstructed in some way. If controller  1408  determines that the motor current does not exceed the first current threshold, the method  2020  may revert to step  2024  and controller  1408  may continue to maintain the motor at a constant speed. If, on the other hand, controller  1408  determines that the motor current exceeds the first current threshold, method  2020  may proceed to step  2028 . 
     At step  2028 , controller  1408  may reduce the motor voltage to maintain the motor current below a second current threshold. In some embodiments, the second current threshold may be greater than the first current threshold and may more closely correlate to the maximum torque that may be safely generated by the motor. In some embodiments, the second current threshold may be less than, or the same as, the first current threshold. In the event that the injection sequence is obstructed, the motor speed may slow and the motor impedance may decrease. As the motor impedance decreases, a lower voltage may be required to maintain the motor current below the second current threshold. Controller  1408  may monitor an average motor voltage applied to the motor. The average motor voltage may be, for example, a time average. 
     Steps  2024  through  2028  of method  2020  may generally be illustrated by the graph depicted in  FIG.  20 B , in which a curve representing a relationship between the voltage applied to the motor of translation mechanism  1366  and the current consumed by the motor is plotted. The curve may be characterized by the following equation: 
     
       
      
       V=iR+V 
       emf  
      
     
     In the equation above, V is the voltage applied to the motor, i is a current consumed by the motor, R is a coil resistance of the motor, and V emf  is a back electromotive force that acts against the applied voltage at a given speed. As shown in  FIG.  20 B , the curve may include a constant speed region, in which the motor may be maintained a constant speed (step  2024 ). In the constant speed region, V emf  may remain approximately constant and the curve may be approximately linear. 
     As shown in  FIG.  20 B , as a load (i.e. a torque) acting on the motor of translation mechanism  1366  increases, the current consumed by the motor may increase. As the current approaches a Max Current, a voltage applied to the motor may be reduced, thereby maintaining the current below the Max Current (steps  2026  and  2028 ). The current consumed by the motor may be maintained below the Max Current using proportional integral (PI) regulation. As shown, there may be a minimum voltage for the motor below which the motor may stall. 
     Steps  2030  through  2038  of method  2020  may correspond to a control sequence for preventing stalling of the motor.  FIG.  20 A  depicts a graph which may represent the voltage applied to the motor and the current consumed by the motor over time and in accordance with steps  2030  through  2038 . 
     At step  2030 , controller  1408  may determine whether the average motor voltage has decreased below a first threshold voltage. The average motor voltage decreasing below the first threshold voltage may indicate that the injection sequence is obstructed. If controller  1408  determines that the average motor voltage has not decreased below a first threshold voltage, method  2020  may revert to step  2028 , at which controller  1408  may continue to maintain the motor current below the second current threshold.  FIG.  20 A  illustrates five intervals during which controller  1408  may maintain the motor current at a constant value (e.g. below the second current threshold): between about 35 seconds and about 37 seconds, between about 39 seconds and about 41.5 seconds, between about 43.5 seconds and about 46 seconds, between about 48 seconds and about 50.5 seconds, and between about 52.5 seconds and about 55 seconds. As shown in  FIG.  20 A , the voltage applied to the motor during each interval may decrease, albeit with some fluctuations, to maintain the motor current below the second current threshold. Though the voltage during each interval in  FIG.  20 A  is shown as decreasing, the voltage need not necessarily decrease to maintain the motor current below the second current threshold, but instead may stay flat in certain situations. 
     If, on the other hand, controller  1408  determines that the average motor voltage has decreased below the first threshold voltage, controller  1408  may cause the injection sequence to be paused for a first time interval. When causing the injection sequence to be paused, controller  1408  may cease applying voltage to the motor. In some embodiments, the first time interval may be 2 seconds, for example.  FIG.  20 A  illustrates four such pauses: between about 37 seconds and about 39 seconds, between about 41.5 seconds and about 43.5 seconds, between about 46 seconds and about 48 seconds, and between about 50.5 seconds and about 52.5 seconds. 
     The first time interval may be sufficiently long to allow fluid pressure within auto-injector  2  to dissipate. The first time interval may also be sufficiently short such that the user may not be prompted to remove auto-injector  2  from the user&#39;s skin (e.g., the first time interval is set to be less than a typical reaction time of the user to falsely identify the end of the injection). The first time interval may further be indicated by illumination of one or more of the LEDs of the progress ring or another light within auto-injector  2  and visible by a user. The LEDs may be illuminated, for example, in a particular pattern or according to a particular color scheme to indicate the first time interval and that the injection sequence is paused rather than stopped. 
     After pausing the injection sequence, controller  1408  may continue the injection sequence at step  2034 . To continue the injection sequence, controller  1408  may resume supplying voltage to the motor of translation mechanism  1366 . At step  2036 , controller  1408  may determine whether the average motor voltage has decreased below the first threshold voltage within a second time interval. The second time interval may be shorter than the first time interval and may be set and/or determined to be indicative of a confirmation that the injection sequence is obstructed. The second time interval may be, for example, about 0.9 seconds. If the motor voltage has not decreased below the first threshold voltage within the second time interval, method  2020  may revert to step  2030 . If, on the other hand, controller  1408  determines that the motor voltage has decreased below the first threshold voltage within the second time interval, method  2020  may proceed to step  2038  at which controller  1408  may cause the injection sequence to be aborted. 
     In some embodiments, controller  1408  may perform step  2026  continuously as it performs steps  2028  to  2036 . For example, controller  1408  may continue to determine whether the motor current exceeds the first current threshold as steps  2028  to  2036  are performed. If the motor current continues to exceed the first current threshold, method  2020  may proceed through steps  2028  to  2036  as described herein previously. In the event the motor current falls below the first current threshold, on the other hand, method  2020  may revert to step  2024  and controller  1408  may maintain the motor at a constant speed. In other words, if a high load on the motor, due to obstruction, high fluid pressure, or the like, dissipates during performance of steps  2028  to  2036 , controller  1408  may simply revert to maintaining a constant motor speed rather than proceeding through any remaining steps unnecessarily. 
     Accordingly, method  2020  may allow controller  1408  to effectively distinguish between situations in which the needle may be partially blocked or a high friction force may be acting against the injection sequence, and situations in which the injection sequence is insurmountably obstructed. In the former situations, auto-injector  2  may have the ability to complete the injection sequence and the injection sequence may not be prematurely terminated. In the latter situations, auto-injector  2  may not have the ability to complete the injection sequence and the injection sequence may be appropriately terminated. In such situations, auto-injector  2  may emit an audio tone and/or illuminate one or more LEDs to indicate that the injection was terminated before completion. Method  2020  may further appropriately terminate an injection sequence in which the piston  1316  extends completely, indicating that the cartridge  1302  is empty. Method  2020  may further allow the auto-injector  2  to be used on an emergency basis if, for example, a user performs an injection without first warming up auto-injector  2  to decrease a viscosity of the medicament. Method  2020  may further allow an injection of a viscous medicament to proceed at a slower rate than the motor and gear reduction ratio may otherwise allow. 
       FIG.  21    shows an exemplary method  2100  of detecting an end of a dose of medicament using emitter  1414  and detector  1416 . Method  2100  may be used, for example, to detect a time at which a full dose of medicament has been dispensed to a user and end the corresponding injection sequence. 
     At step  2102 , controller  1408  may initiate an injection sequence. As described herein previously, an injection sequence may be initiated upon depressing activating switch  1409  against a user&#39;s skin and/or detecting the user&#39;s skin by touch sensor  1410 . At step  2104 , controller  1408  may cycle emitter  1414  on and off periodically. Emitter  1414  may be cycled on and off rapidly in a square wave pattern, such that emitter  1414  is turned off and on several times per second. Cycling emitter  1414  on and off may allow detector  1416  to be exposed to light produced by emitter  1414  in combination with ambient light, and also to ambient light alone. 
     At step  2106 , controller  1408  may receive a first signal from detector  1416  corresponding to a time when emitter  1414  is off. The first signal may correspond to, and/or be indicative of, ambient light detected by the detector  1416 . At step  2108 , controller  1408  may receive a second signal from detector  1416  corresponding to a time when emitter  1414  is on. The second signal may correspond to, and/or be indicative of, light emitted by emitter  1414  in combination with ambient light as detected by the detector  1416 . 
     At step  2110 , controller  1408  may calculate a difference between a first light value represented by the first signal and a second light value represented by the second signal. The difference may be indicative of how much light detected by detector  1416  is attributable to light emitted by emitter  1414  as opposed to ambient light. At step  2112 , controller  1408  may determine whether the difference is less than a threshold value. If controller  1408  determines that the difference is not less than a threshold value, method  2100  may revert to step  2106 . If, on the other hand, controller  1408  determines that the difference is less than the threshold value, controller  1408  may end the injection sequence at step  2114 . 
     Accordingly, method  2100  may be used to reduce the impact of ambient light when detecting an end of a dose of medicament. Specifically, method  2100  may address a situation in which light from emitter  1414  is blocked from reaching the detector  1416  indicating an end of a dose, yet ambient light is able to reach detector  1416  and create a false negative reading indicating that an end of dose has not been reached. 
       FIG.  22    shows another exemplary method  2200  of detecting an end of a dose of medicament using emitter  1414  and detector  1416 . Method  2200  may be used, for example, to detect a time at which a full dose of medicament has been dispensed to a user and end the corresponding injection sequence. 
     At step  2202 , controller  1408  may initiate an injection sequence. As described herein previously, an injection sequence may be initiated upon depressing activating switch  1409  against a user&#39;s skin and/or detecting the user&#39;s skin by touch sensor  1410 . At step  2204 , controller  1408  may initiate emitter  1414  or otherwise cause emitter  1414  to emit light. 
     At step  2206 , controller  1408  may cause the injection sequence to continue for a first period of time. The first period of time may be a predetermined period of time corresponding to a duration in which a full dose cannot possibly be, or is unlikely to be, dispensed. For example, the first period of time may be between about 20% and 50% of the total injection time. During the first period of time, controller  1408  is not able to interrupt the injection sequence in response to a signal received from detector  1416  (but could still interrupt the injection sequence due to obstructions or stalling as discussed with reference to  FIG.  20   ). 
     At step  2208 , after the end of the first period of time, controller  1408  may determine whether an amount of light received by detector  1416  is less than a first threshold light value. Controller  1408  may make the determination based on a signal received from detector  1416  indicative of light received by detector  1416 . The first threshold light value may correspond to an amount of light received by detector  1416  at the end of a dose. If controller  1408  determines that the amount of light received by detector  1416  is not less than the first threshold light value, controller  1408  may continue the injection sequence and method  2200  may otherwise remain at step  2208 . If, on the other hand, controller  1408  determines that the amount of light received by detector  1416  is less than the first threshold light value, the method may proceed to step  2210 . 
     At step  2210 , controller  1408  may determine whether the amount of light received by detector  1416  is greater than or equal to the first threshold light value. If controller  1408  determines that the amount of light received by detector  1416  has risen to or above the first threshold light value, controller  1408  may continue the injection sequence and method  2200  may revert to step  2208 . If, on the other hand, controller  1408  determines that the amount of light received by detector  1416  has remained less than the first threshold light value, the method may proceed to step  2212 . Step  2210  may in effect enable controller  1408  to “clear” the injection sequence of anomalous interruptions of the light received by the detector, which may be caused by an air bubble within cartridge  1302  that blocks the path of light between emitter  1414  and detector  1416 , for example, provided the amount of light subsequently meets or exceeds the first threshold light value. 
     At step  2212 , controller  1408  may determine whether the motor current exceeds a first threshold current value. The first threshold current value may be determined and/or set based on a current indicative of an end of the injection sequence. The first current threshold value may be set, for example, based on a current indicative of piston  1316  reaching second end  1306  of cartridge  1302 . If controller  1408  determines that the motor current does not exceed the first threshold current value, controller  1408  may continue the injection sequence and method  2200  may revert to step  2208 . If, on the other hand, controller  1408  determines that the motor current exceeds the first threshold current value, method  2200  may proceed to step  2214  at which controller  1408  may cause the injection sequence to end. 
     Method  2200  may accordingly allow for accurate identification of the end of an injection sequence by identifying an instant in which both the light received by detector  1416  and the motor current are indicative of an end of the dose. By performing steps  2208 ,  2210 , and  2212  sequentially, false identifications of the end of the dose due to either anomalous interruptions of light or anomalous high current events alone may be mitigated. Method  2200  may specifically reduce the impact of bubbles within cartridge  1302  on detection of the end of a dose of medicament. 
       FIG.  23    shows an exemplary method  2300  of operating activating switch  1409  of auto-injector  2  according to the disclosure. In particular,  FIG.  23    depicts an exemplary sequence of positions of activating switch  1409  and corresponding functions of auto-injector  2 . 
     Initially, at step  2302 , auto-injector  2  may be disposed within a packaging such that plunger  1450  is in a depressed state and auto-injector  2  is in a low-power sleep mode. In some embodiments, during manufacturing auto-injector  2  may be programmed in an awake or active state. In some embodiments, if plunger  1450  is depressed for a predetermined period of time following programming, such as when auto-injector is placed in the packaging, auto-injector  2  may be configured to transition to the low-power sleep mode. The predetermined period of time may be any suitable period of time, such as 60 minutes, 30 minutes, 15 minutes, 10 minutes, 5 minutes, 2 minutes, or any other suitable period. Auto-injector  2  may be sealed in the packaging such that the packaging indicates that the auto-injector  2  has not been previously used. The packaging may be made from any suitable material, including paper, cardboard, plastic, cellophane, and the like. The packaging may press against plunger  1450  such that plunger  1450  is flush or nearly flush with housing  3  of auto-injector  2  and plunger  1450  is blocked from extending outwardly from auto-injector  2 . With plunger  1450  in the depressed state, the circuit associated with activating switch  1409  may be open, thereby maintaining the auto-injector  2  in the low-power sleep mode. 
     At step  2304 , auto-injector  2  may be removed from the packaging such that plunger  1450  is no longer depressed by the packaging and plunger  1450  may extend outwardly from the auto-injector  2 . As plunger  1450  transitions from the depressed state to the free or extended state, plunger flange  1454  may contact or otherwise depress plunger switch  1448 , thereby completing the circuit associated with activating switch  1409 . 
     At step  2306 , in response to the circuit associated with activating switch  1409  being completed, auto-injector may transition from the low-power sleep mode to an active mode. In the active mode, auto-injector  2  may calibrate touch sensor  1410 . Auto-injector  2  may calibrate touch sensor  1410  by detecting a value or measurement of the touch sensor  1410  in ambient air, i.e. not against a user&#39;s skin. Auto-injector  2  may perform such calibration during a predetermined time period after auto-injector  2  is removed from the packaging (in some cases immediately after removal) so that such calibration occurs before a user may expose their skin to touch sensor  1410 . In the active mode, auto-injector  2  may further detect whether emitter  1414  and/or detector  1416  are functioning properly, detect whether a needle is positioned properly, detect whether the motor of translation mechanism  1366  is responsive and/or operational, and/or perform any other suitable status tests. Auto-injector  2  may detect the positioning of the needle, for example, using a switch or detector configured to report the position of the needle to the controller  1408 . In the active mode, auto-injector  2  may further illuminate one or more backlights to allow a user to inspect a vial and/or a drug contained in the vial through transparent window  50 . In the active mode, auto-injector  2  may further display any other indication that auto-injector  2  is ready to be used. 
     At step  2308 , auto-injector  2  may be placed against a user&#39;s skin such that plunger  1450  is depressed into auto-injector  2 . Upon plunger  1450  being depressed, the circuit associated with activating switch  1409  may transition to an open state. As described above with reference to  FIG.  18    and method  2000 , auto-injector  2  may further detect contact with skin using touch sensor  1410 . In response to depression of plunger  1450  and detection of contact with skin, auto-injector  2  may initiate an injection sequence at step  2310 . The injection sequence may be a sequence resulting in injection of the user with a medicament, as described herein previously. 
     At step  2312 , auto-injector  2  may be removed from the user&#39;s skin and plunger  1450  may again extend outwardly from auto-injector  2 . Upon plunger  1450  extending outwardly, the circuit associated with activating switch  1409  may transition from the open state to the closed state. In response, auto-injector  2  may end the injection sequence at step  2310  and, for example, initiate retraction of the patient needle by reversing the motor. Auto-injector  2  may initiate retraction of the needle if the injection sequence has proceeded to completion or if the auto-injector has prematurely or accidentally been removed from the skin to prevent wet injection. Alternatively, in some embodiments, controller  1408  may determine whether a value received from touch sensor  1410  is indicative of the auto-injector  2  remaining in contact with the user&#39;s skin. If the value received by controller  1408  is indicative of the auto-injector  2  remaining in contact with the user&#39;s skin, auto-injector  2  may pause the injection sequence, thereby preventing wet injection. If the plunger  1450  is again depressed, thereby placing the circuit associated with activating switch  1409  in the open state, auto-injector  2  may resume the injection sequence. 
     According to the foregoing method  2300 , activating switch  1409  may serve to keep auto-injector  2  in a lower-power sleep mode when in the packaging, transition auto-injector  2  to an active mode upon removal from the packaging, indicate when auto-injector  2  has been placed against a user&#39;s skin for an injection sequence, and indicate when auto-injector  2  has been removed from the user&#39;s skin at the end of an injection sequence. Moreover, a signal from activating switch  1409  may be cross-checked against a signal from touch sensor  1410  to more accurately determine whether auto-injector  2  has been removed from the user&#39;s skin, or whether, for example, an inadvertent or minor movement of auto-injector occurred. 
     It should be understood that steps of one or more of the various methods described herein may be combined in certain embodiments. Furthermore, in certain embodiments, fewer than all of the steps of a method described herein may be performed and/or additional steps not described herein may be performed. Moreover, the steps described herein need not necessarily be performed in the exact order presented. 
     Notably, reference herein to “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included, employed and/or incorporated in one, some or all of the embodiments of the present disclosure. The usages or appearances of the phrase “in one embodiment” or “in another embodiment” in the specification are not referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of one or more other embodiments, nor limited to a single exclusive embodiment. The same applies to the terms “implementation,” and “example.” The present disclosure are neither limited to any single aspect nor embodiment thereof, nor to any combinations and/or permutations of such aspects and/or embodiments. Moreover, each of the aspects of the present disclosure, and/or embodiments thereof, may be employed alone or in combination with one or more of the other aspects of the present disclosure and/or embodiments thereof. For the sake of brevity, certain permutations and combinations are not discussed and/or illustrated separately herein. 
     Further, as indicated above, an embodiment or implementation described herein as “exemplary” is not to be construed as preferred or advantageous, for example, over other embodiments or implementations; rather, it is intended convey or indicate the embodiment or embodiments are example embodiment(s). 
     The present disclosure is further described by the following non-limiting items: 
     Item 1. An injection device, comprising: 
     a housing; 
     a container disposed within the housing, the container enclosing a fluid and having a first end and a second end; 
     a conduit movable relative to the container, wherein the conduit is not in fluid communication with the fluid enclosed by the container while in a first position, and is in fluid communication with the fluid enclosed by the container and configured to deliver the fluid from the container to a patient while in a second position; 
     a lock that is removable from the housing, the lock having a first portion and a second portion, wherein:
         in a first configuration where the lock is coupled to the housing, the first portion of the lock is disposed exterior of the housing and the second portion of the lock is disposed within the housing between the container and the conduit;   in the first configuration, the conduit is prevented from moving into fluid communication with the fluid enclosed by the container by the second portion of the lock; and   in a second configuration where the lock is removed from the injection device, the conduit is able to move into fluid communication with the fluid enclosed by the container.       

     Item 2. The injection device of item 1, further including: 
     an adhesive disposed exterior of the housing; and 
     a cover disposed over the adhesive, wherein the cover is removable from the injection device to expose the adhesive, 
     wherein the lock is coupled to the cover such that the lock is removed from the injection device when the cover is removed from the injection device. 
     Item 3. The injection device of item 1, further including a controller and a skin sensor coupled to the controller, wherein: 
     the skin sensor is configured to detect when skin is in contact with an outer surface of the housing adjacent to the skin sensor; 
     the controller is configured to cause the conduit to move into fluid communication with the fluid enclosed by the container; and 
     when the lock is coupled to the housing in the first configuration, the first portion of the lock is configured to prevent skin from contacting the outer surface of the housing adjacent to the skin sensor. 
     Item 4. The injection device of item 1, wherein, while in the first configuration, the lock is configured to prevent inadvertent activation of the injection device when the injection device is dropped or subject to vibration. 
     Item 5. An injection device, comprising: 
     a housing; 
     a plunger coupled to the housing and movable relative to the housing; 
     one or more electronics components used during an injection performed by the injection device, the one or more electronics components being formed within an electrical circuit, wherein:
         in a first configuration, a first portion of the plunger is disposed within the housing, the electrical circuit is open, and the one or more electronics components are in a low-power sleep mode;   in a second configuration, the plunger moves outward relative to the housing, and the first portion of the plunger extends exterior of the housing; and   in the second configuration, the electrical circuit is closed, and the one or more electronics components are transitioned from the low-power sleep mode, to an active mode.       

     Item 6. The injection device of item 5, further comprising a biasing member movable from a resting position to a stressed position, wherein: 
     in the first configuration, the biasing member is in the stressed position; and 
     in the second configuration, the biasing member is in the resting position. 
     Item 7. The injection device of item 6, further including a stop configured to maintain the biasing member in the stressed position and the plunger in the first configuration when the stop is in a blocking position, wherein movement of the stop from the blocking position allows the biasing member to move to the resting position and the plunger to move to the second configuration. 
     Item 8. The injection device of item 7, wherein the stop includes a packaging of the injection device. 
     Item 9. The injection device of item 5, wherein the one or more electronics components include a switch, and transition of the plunger from the first configuration to the second configuration moves the switch to close the electrical circuit. 
     Item 10. The injection device of claim  5 , wherein: 
     the plunger is movable from the second configuration toward the housing to a third configuration; and 
     the injection device is configured to initiate an injection by the injection device only after the plunger is moved to the third configuration and the one or more electronics components are in the active mode. 
     Item 11. The injection device of item 10, wherein: 
     the one or more electronics components include a skin sensor and the injection device further includes a controller configured to initiate the injection by the injection device; 
     the skin sensor is configured to detect a presence of skin in contact with an outer surface of the housing adjacent to the skin sensor only after the plunger has moved to the third configuration; and 
     the controller is configured to initiate the injection only after detection of skin by the skin sensor. 
     Item 12. The injection device of item 11, further including a motor configured to dispense medicament from the injection device during the injection, wherein: 
     during the injection, the plunger is movable from the third configuration, away from the housing, to a fourth configuration; and 
     the controller is configured to cease operation of the motor while the motor is operating and the controller senses the plunger has moved from the third configuration to the fourth configuration. 
     Item 13. The injection device of item 12, wherein the controller is configured to: 
     determine that skin has remained in contact with the outer surface of the housing adjacent to the skin sensor, while the plunger is in the fourth configuration; and 
     resume operation of the motor when the plunger moves from the fourth configuration to the third configuration, after the controller determines that skin has remained in contact with the outer surface of the housing adjacent to the skin sensor while the plunger was in the fourth configuration. 
     Item 14. An injection device, comprising: 
     a housing, wherein the housing includes a curved bottom surface that is concave when viewed from a point external to the housing that is closer to the bottom surface of the housing than a top surface of the housing; 
     a circuit board positioned adjacent to the bottom surface of the housing, wherein the circuit board includes a skin sensor configured to sense a presence of skin in contact with the bottom surface of the housing; and 
     a controller coupled to the circuit board, wherein the controller is configured to initiate an injection by the injection device only after the skin sensor senses the presence of skin in contact with the bottom surface of the housing. 
     Item 15. The injection device of item 14, wherein the skin sensor is configured to sense the presence of skin in contact with the bottom surface of the housing without skin directly contacting the skin sensor. 
     Item 16. The injection device of item 14, wherein the skin sensor is a capacitance sensor. 
     Item 17. The injection device of item 14, wherein: 
     the housing further includes an opening in the curved bottom surface; 
     the injection device further includes a needle extendable out of the housing through the opening; and 
     the skin sensor is positioned adjacent to the opening. 
     Item 18. The injection device of item 14, wherein the circuit board is the only circuit board disposed within the housing. 
     Item 19. A method of manufacturing an injection device, the method comprising: 
     depositing a first material onto a mold, the first material having a first opacity; 
     depositing a second material around the mold and the first material, the second material having a second opacity that is higher than the first opacity; and 
     positioning a container enclosing a medicament within the injection device and adjacent to a first portion of the injection device formed by the first material. 
     Item 20. The method of item 19, further including positioning one or more LEDs within the injection device and adjacent to one or more second portions of the injection device, separate from the first portion of the injection device, the one or more second portions of the injection device being formed by the first material. 
     Item 21. An injection device, comprising: 
     a container disposed within the housing, the container having a first end and a second end; 
     a piston configured to move from the first end of the container toward the second end of the container to dispense a medicament from the container; 
     a drive member configured to drive the piston through the container; 
     an emitter configured to emit a beam of light toward the container; 
     a detector positioned on an opposing side of the container from the emitter, wherein the detector is configured to receive the beam of light emitted from the emitter; and 
     a controller coupled to the drive member, the emitter, and the detector, the controller being configured to:
         receive a first signal from the detector while the emitter is off, the first signal corresponding to an ambient level of light surrounding the injection device;   receive a second signal from the detector while the emitter is on;   calculate a difference between light values represented by the first signal and the second signal; and   cease operation of the drive member when the difference is less than a threshold value.       

     Item 22. An injection device, comprising: 
     a container disposed within the housing, the container having a first end and a second end; 
     a piston configured to move from the first end of the container toward the second end of the container to dispense a medicament from the container; 
     a drive member configured to drive the piston through the container; 
     an emitter configured to emit a beam of light toward the container; 
     a detector positioned on an opposing side of the container from the emitter, wherein the detector is configured to receive the beam of light emitted from the emitter; and 
     a controller coupled to the drive member, the emitter, and the detector, the controller being configured to:
         initiate the drive member and the emitter;   receive a first signal from the detector while the emitter is on, the first signal being representative of an amount of light received by the detector;   allow for continued operation of the drive member for a first period of time immediately after initiation of the drive member; and   cease operation of the drive member upon determining (1) that the amount of light received by the detector is less than a first threshold light value and (2) before the amount of light received by the detector subsequently rises to or above the first threshold light value, that a current of the drive member is greater than a first threshold current value.       

     Item 23. The injection device of item 22, wherein the controller is further configured to: 
     continue operation of the drive member if the determined amount of light received by the detector is less than the first threshold value and, before the current of the drive member exceeds the first threshold current value, the amount of light received by the detector rises to or above the first threshold light value. 
     Item 24. An injection device, comprising: 
     a container disposed within the housing, the having a first end and a second end; 
     a piston configured to move from the first end of the container toward the second end of the container to dispense a medicament from the container; 
     a drive member configured to drive the piston through the container; and 
     a controller coupled to the drive member, the controller being configured to:
         maintain a speed of the drive member until a current of the drive member exceeds a first threshold; and   after the current of the drive member exceeds the first threshold, reduce a voltage of the drive member to maintain the current of the drive member below a second threshold that is greater than or equal to the first threshold.       

     Item 25. The injection device of item 1, further including a controller and a skin sensor coupled to the controller, wherein: 
     the skin sensor is configured to detect when skin is in contact with an outer surface of the housing adjacent to the skin sensor; 
     the controller is configured to cause the conduit to move into fluid communication with the fluid enclosed by the container; and 
     the injection device further comprises a removable cover configured to prevent skin from contacting the outer surface of the housing adjacent to the skin sensor. 
     Item 26. The method of item 19, further comprising: 
     positioning a conduit movable relative to the container within the injection device such that the conduit is not in fluid communication with the fluid enclosed by the container; 
     wherein the first portion includes a first transparent window through which an interior of the injection device is visible; and 
     wherein the container is visible through the transparent window. 
     Item 27. The method of item 26, wherein the first portion further includes a plurality of second transparent windows arranged on a top surface of the injection device, wherein at least one LED is visible through each of the plurality of second transparent windows; and 
     wherein the first transparent window and the plurality of second transparent windows are collectively formed of a contiguous portion of the first material.