Abstract:
Battery powered systems with long standby times, such as automatic external defibrillators, may be required to indicate their operational status to a user by blinking lights or sounding speakers or buzzers. These active status indication activities consume power thereby reducing the battery life of the system. Automatically adjusting the level and frequency of these indication activities to match the ambient environment can reduce power consumption of the battery operated system. For example, in a dimly lit room, an indicator light may be visible even though it might be too dim to be seen in a bright room. Thus, if the room is dim, indicator lights can be dimmed to conserve power. These automatic adjustments made in response to the environment may help conserve power and extend battery life.

Description:
PRIORITY CLAIM TO PROVISIONAL APPLICATION 
   This application claims priority to provisional patent application entitled, “Environmentally Responsive Active Status Indicator” filed on Mar. 21, 2005 and assigned U.S. Application Ser. No. 60/663,909. The entire contents of the provisional patent application mentioned above are hereby incorporated by reference. 

   TECHNICAL FIELD 
   The present invention is generally directed to battery-powered cardiac defibrillation systems, and relates more particularly to status indicators that conserve battery power by automatically adjusting their operation in response to their environment. 
   BACKGROUND OF THE INVENTION 
   Automatic external defibrillators (AEDs) are defibrillators that are designed to be operated by users with minimal training. Because AEDs can be used by non-medical personnel to treat sudden cardiac arrest (SCA), they are being deployed in a myriad of locations outside of traditional medical settings. As a result, more and more non-medical establishments are purchasing AEDs for deployment in their environments. AEDs are typically powered by stand alone battery systems. 
   AEDs are typically standby devices that are used infrequently and that remain in storage for long periods of time. This standby storage time can be on the order of months or even years. Minimizing power consumed by the AED while it is in standby mode during storage may extend the battery life of the system and reserve battery power for rescue attempts using the AED. 
   Since AEDs are in standby mode for long periods of time, knowing the operational status of a standby AED is very important. The operational status of an AED can be determined by various internal self tests. These tests may cover general operations, battery life, memories, software, etc. The results of these tests can be communicated to a user via visual or aural indicators even while the AED is in a low power standby mode. In such a system, there can be a status circuit or apparatus inside the AED that can report the status of the AED system. More generally, the AED may be referred to as the host system or host device. Various systems other than AEDs have similar low power consumption requirements for status indicators. Such systems may be referred to as host systems or host devices when they include status circuits that indicate the status of the host system. 
   Status indicators for host systems may be passive or active. An active indicator is one that may require power to be expended for it to continue to indicate, such as an indicator light. A passive indicator may continue to indicate without consuming additional power. For example, an indicator that mechanically changes colors by physically flipping an internal element that can be seen by a user through a window may be a passive indicator. Once the internal element of the passive indicator is physically flipped, it will stay in that state without additional power. 
   Active indicators can include lights, light emitting diodes (LEDs), video screens, speakers, or buzzers. Active indicators have the disadvantage of continuing to use power over time, but they can allow host status to be more readily determined in a wide variety of ambient conditions. For example, an active indicator may illuminate a green light to indicate that its battery is healthy, or a red light when its battery needs replacement. This repeated illumination of a light requires power, but may be much more likely to catch the attention of a user than a passive indicator would. This may be particularly true if the device is stored in a dark or low-visibility environment. 
   For battery powered, standby devices, such as AEDs, conservation of battery power is an important design goal. Such systems that use active status indicators have the additional challenge of reducing the amount of power they expend operating the status indicators. Since these devices may be stored, in standby mode, in a variety of environments there are times when the power used for status indication is excessive. For example, if a status light is designed to be bright enough to be seen in a well lit room, it may be much brighter than necessary when in a dark room or when stored in a cabinet, carrying case or car trunk. 
   Similarly for an aural status indicator, if the volume level of the indicator has adequate magnitude for a noisy environment, such magnitude may be much higher than necessary in a quiet room setting and therefore consume more power than necessary. Because of the importance of conserving battery life in systems with long standby requirements, such as AEDs, there is a need for status indicators that may sense their operating environment and then adjust accordingly either, or both, indicator intensity or indication event frequency. 
   SUMMARY OF THE INVENTION 
   The inventive active status indicator (ASI) system can indicate a status of a host device while the host device is in a non-operative state. The operation of the ASI system may automatically adjust indicators in response to sensing environmental conditions of the host device while the host device is in the non-operative state. A non-operative state of the host device usually includes situations in which the host device is performing less than all of its primary functions. For example, a non-operative state for automatic external defibrillators (AEDs) usually includes situations in which an AED is not performing a rescue on a patient. Functions that may occur during non-operative states in AEDs may include self-tests and active status indicator events. 
   The inventive ASI system may supply status information about the host device to a user. When the host device is operational, the ASI system may also supply the host device with environmental conditions sensed by the ASI system. The host device can query the ASI system for these parameters when the host device is in an operational state. 
   While the host device is in the non-operative state, the inventive ASI system can adjust the intensity level, duration of powering, or duration between powering, or any combination thereof, for status indication. These adjustments can reduce power consumed by the ASI system. Battery operated devices with long stand-by requirements, such as an automatic external defibrillator (AED), may benefit from increased battery life because of power conserving features of the inventive ASI system. 
   The inventive ASI system may also operate in a low power standby or sleep mode while the host device is also in a standby mode. However, the low power standby mode of the ASI system is different from the standby mode of the host device in that the ASI system can be “awakened” from its standby mode. Meanwhile, the host device becomes fully operational when it is switched from its standby mode or “off” mode. 
   The inventive ASI system can indicate the status of a host device by using illuminated indicators, indicator lights, audible speakers, or other outputs to a user. The intensity level of the indicator can be automatically adjusted to one that is appropriate for the environment. The inventive system can use light sensors, microphones, or other sensors to detect the environment and adjust the indicator accordingly. For example, the inventive ASI system may sense that a room is dark and then lower the brightness of an indicator light. In a brighter room, the inventive ASI system may increase the intensity of an indicator light so that it can still be seen. 
   In the case of an audible indicator, the inventive ASI system may sense the noise level in the room and then adjust the volume of the audible indicator output as needed. Supplying only the level of indication that a situation requires, may consume considerably less power than always supplying the maximum level of indication. This power savings can extend the battery life of battery-operated host devices. 
   The inventive ASI system may change the delay between indicator events in response to the environment. For example, if the room is extremely quiet, there might not be anyone present to see or hear an indicator event. Thus, the ASI may reduce power consumption by illuminating a light or chirping a speaker less frequently. Each illumination of the light or sounding of a speaker may be referred to as an indicator event. 
   The inventive ASI system may detect when the host device is enclosed, such as in a case, cabinet or car trunk and use this information to reduce the intensity or frequency of the status indicators. The ASI may cease indicator functions entirely in such environments. For host devices that are stored away until needed, this ASI functionality may significantly extend battery life. A common example of such a situation is an AED enclosed in a non-transparent or opaque, hard case where it is readily accessible during an emergency. 
   The inventive ASI system may detect when the host device is enclosed using a switch or magnetic detector. As an example of a magnetic detector, a reed switch in the host device may align with a magnet affixed to the case or enclosure. This can indicate to the inventive ASI system that the host device is in a specific environmental situation and indicator outputs should be adjusted accordingly. For example, if the host device is stored in an opaque carrying case, there may be no need to illuminate any indicator lights. Ceasing or reducing indicator events which might be unnecessary can significantly extend battery life of the host device. 
   The inventive ASI system may use reflections to detect when the host device is enclosed. If a large enough percentage of the light emitting from an indicator light of the host device is reflected right back into the light sensor of the host device, there may be a high likelihood that a cabinet or enclosure wall just outside the host device is providing a reflective surface. This capability may be used by the inventive ASI system to reduce or cease the indicator events and thus conserve power. 
   In addition to reacting to environmental conditions, the inventive ASI system may also adjust indicators in response to internal events of the host device. The ASI system may reduce indicator intensity levels, duration of powering for an indicator, and increase delays between indicator events if a battery level of the host device is below a certain threshold. In such situations, the host device can detect low battery power status during normal operations and set a flag that can be checked by the ASI system. The ASI can adjust indicator operations in response to this flag in order to prevent rapid discharge of the remaining battery power. 
   The inventive ASI system, according to another exemplary aspect, may not detect environmental conditions every time a status indicating event is scheduled to occur. That is, the inventive ASI system can detect environmental conditions such as ambient light conditions or ambient acoustic noise conditions at a rate that can be different than a rate set for an indicating event. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a plan view of an AED according to one exemplary embodiment of the invention. 
       FIG. 2  is a functional block diagram illustrating the ASI processor and an environmentally responsive LED indicator according to one exemplary embodiment of the invention. 
       FIG. 3  is a functional block diagram illustrating the ASI processor and an environmentally responsive audible indicator according to one exemplary embodiment of the invention. 
       FIG. 4  is a functional block diagram illustrating the relationship between the ASI processor and the host processor according to one exemplary embodiment of the invention. 
       FIG. 5  is a logic flow diagram highlighting exemplary steps for an ASI processor in a system with environmentally responsive active status indicators according to one exemplary embodiment of the invention. 
       FIG. 6A  is a logic flow diagram illustrating an exemplary routine for sensing the environment in a system with a visual ASI that is environmentally responsive according to one exemplary embodiment of the invention. 
       FIG. 6B  is a logic flow diagram illustrating an exemplary routine for sensing the environment in a system with an auditory ASI that is environmentally responsive according to one exemplary embodiment of the invention. 
       FIG. 7A  is a logic flow diagram illustrating an exemplary routine for setting the indicator intensity and frequency in a system with a visual ASI that is environmentally responsive according to one exemplary embodiment of the invention. 
       FIG. 7B  is a logic flow diagram illustrating an exemplary routine for setting the indicator intensity and frequency in a system with an auditory ASI that is environmentally responsive according to one exemplary embodiment of the invention. 
       FIG. 8  is an elevation view illustrating a surface-mounted LED and surface-mounted photodiode both optically coupled to the same light pipe according to one exemplary embodiment of the invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The inventive ASI system may comprise an active status indicator (ASI) whose operation is automatically adjusted in response to its environment while the host device is in a non-operative state. The inventive ASI system may supply status information about a host device to a user while the host device is in a non-operative state. The inventive ASI system may adjust the intensity level, duration of powering, or duration between powering of any status indication in response to the ambient environment of the host system. Such adjustments may reduce power consumed by the ASI system thereby extending battery life of the ASI system and the host device. 
   The inventive ASI system may indicate the status of a host device using illuminated indicators, indicator lights, audible speakers, or other outputs to a user. The intensity level, duration of powering, or duration between powering, or any combination thereof, of the indicators may be automatically adjusted to one that is appropriate for the environment. The inventive system may use light sensors, microphones, or other sensors to detect the environment and adjust the indicator accordingly. 
   The inventive system may comprise an ASI processor which may comprise a microcontroller with a low-power sleep mode for sensing the environment and controlling the active indicators accordingly. The inventive ASI system is designed to substantially minimize or eliminate all activity and power consumption during its sleep mode. The ASI processor may also be used to support other functions of the host system such as an on/off switch response, self test operations, or controlling the operational state of the host systems main processor. 
   The inventive ASI system may use reflections of its own status indicators to determine when the host system in physically enclosed. The level of light or sound from an indicator that is reflected back to the host may be an indication of the host system being physically enclosed. Such an indication may be used to further reduce, or possibly disable, any power dedicated to driving active status indicators. 
   Turning now to the drawings, in which like reference numerals refer to like elements,  FIG. 1  illustrates a plan view of an AED  100  with an environmentally responsive ASI system according to one exemplary embodiment of the invention. Even while AED  100  is in standby mode, light-pipe  140  can be illuminated by LED  235  (see  FIG. 2 ) which may serve as an active status indicator (ASI) for AED  100 . Speaker  160  may also provide active status indication. Additionally, speaker  160  may provide instructions or other information. Connector  120  can connect patient electrodes (see  FIG. 1 ) to AED  100 . 
   The patient electrodes can be used to monitor ECG information from a patient to determine if the patient&#39;s cardiac rhythm is suitable for defibrillation shock. If so, the operator may be instructed to press button  150  to initiate an electrical shock through the patient electrodes attached at connector  120 . The outer housing  110  of AED  100  may contain and protect the electronic components of AED  100  including ASI circuit  200  (see  FIG. 2 ). 
   An on/off button  130  can be used to power AED  100  into an operational mode or transition AED  100  into standby mode. While the on/off button  130  appears to the user to turn off AED  100  completely, the on/off button  130  may actually turn off power to a host processor  410  (See  FIG. 4 ) while placing an ASI processor  210  (See  FIG. 4 ) into its very low power sleep mode or standby mode. 
   Referring now to  FIG. 2  which illustrates a functional block diagram of an environmentally responsive ASI circuit  200  according to one exemplary embodiment of the invention, an LED light  235  is used as an active visual indicator. ASI processor  210  may comprise a general processor such as the MSP430F1232, an ultra-low-power microcontroller, made by Texas Instruments. However, one of ordinary skill in the art will appreciate that ASI processor  210  may comprise a microcontroller, microprocessor, DSP processor, application specific logic, programmable logic, or numerous other forms without departing from the spirit and scope of the invention. Battery  220  powers the ASI circuit  200 . ASI processor  210  may spend most of the time in a low-power sleep mode. Timers (not illustrated), which may be internal or external to processor  210 , wake processor  210  every few seconds to allow it to briefly illuminate LED  235  thereby providing a status indication. 
   Prior to illuminating LED  235 , ASI processor  210  samples light sensor  240  to determine the ambient light level around the host device. LED driver  230  can control the intensity, or brightness, level of LED  235 . LED driver  230  may control this intensity using a pulse width modulation (PWM) technique when driving LED  235 . ASI Processor  210  sets this intensity level based on ambient light levels sampled from sensor  240 . Light pipe  140  may be a translucent plastic element that optically couples LED  235  and light sensor  240  to the outside of system housing  110 . An exemplary application of the inventive ASI system can comprise the periodic illumination of LED  235  in a green state to indicate that the host system is operating properly and further comprise changing the illumination state of LED  235  to red if the host system requires operator attention. Operator attention may be required, for example, because of a failed internal self test or a low charge detected on battery  220 . 
   Referring now to  FIG. 3  which illustrates a functional block diagram of an environmentally responsive ASI circuit  300  according to one exemplary embodiment of the invention, sound from a speaker  160  is used as an active, aural indicator. Battery  220  powers the ASI circuit  200 . ASI processor  210  may spend most of the time in a low-power sleep mode. Timers (not illustrated), which may be internal or external to processor  210 , wake processor  210  every few seconds to allow it to sound speaker  160  thereby providing a status indication. Prior to sounding speaker  160 , ASI processor  210  samples microphone  340  to determine the ambient noise level around the host device. Speaker driver  330  can control the volume, or loudness, of speaker  160 . Processor  210  sets this volume level based on ambient noise levels sampled from microphone  340 . 
   Referring now to  FIG. 4  which illustrates a functional block diagram  400  illustrating a relationship between ASI processor  210  and host processor  410 . Battery  220  powers the system, including both processors  210  and  410 . ASI processor  210 , which may spend most of the time in a low-power sleep mode, wakes every few seconds to sample sensors  430  and actuate indicators  420 . ASI processor  210  may also wake periodically to perform, or cause to be performed, built in self tests of the host system. ASI processor  210  may also monitor power button  130  in order to turn host processor  410  on and off. Sensors  430  may comprise light sensor  240  (see  FIG. 2 ) and also may comprise microphone  340  (see  FIG. 3 ). Indicators  420  may comprise LED  235  (see  FIG. 2 ) and may also comprise speaker  160  (see  FIG. 3 ). 
     FIG. 5  illustrates a logical flow diagram  500  of a method for reducing power consumption by an active status indicator (ASI) and extending battery life for a host system. Logical flow diagram  500  highlights some key functional features of ASI processor  210 . One of ordinary skill in the art will appreciate that process functions of ASI processor  210  may comprise firmware code executing on a microcontroller, microprocessor, or DSP processor; state machines implemented in application specific or programmable logic; or numerous other forms without departing from the spirit and scope of the invention. In other words, the invention may be provided as a computer program which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic devices) to perform a process according to the invention. 
   The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing electronic instructions. 
   Certain steps in the processes or process flow described in all of the logic flow diagrams referred to below must naturally precede others for the invention to function as described. However, the invention is not limited to the order of the steps described if such order or sequence does not alter the functionality of the present invention. That is, it is recognized that some steps may be performed before, after, or in parallel other steps without departing from the scope and spirit of the present invention. 
   Further, one of ordinary skill in programming would be able to write such a computer program or identify the appropriate hardware circuits to implement the disclosed invention without difficulty based on the flow charts and associated description in the application text, for example. Therefore, disclosure of a particular set of program code instructions or detailed hardware devices is not considered necessary for an adequate understanding of how to make and use the invention. The inventive functionality of the claimed computer implemented processes will be explained in more detail in the following description in conjunction with the remaining Figures illustrating other process flows. 
   Step  510  is a waiting step. ASI processor  210  can operate by predominantly waiting in a power saving sleep mode to be woken by events that it acts upon briefly before returning to the sleep mode. In the exemplary embodiment of the method illustrated in  FIG. 5 , three events may wake ASI processor  210  from its sleep mode. These events include, but are not limited to, a power button event, an indicator timer event, or a self test event. After handling whichever event awakens ASI processor  210  from the sleep mode of step  510 , the ASI processor  210  can transition back through step  580  into the sleep mode of step  510  where ASI processor  210  waits for the next wake event. 
   In decision step  520 , ASI processor  210  determines what type of event woke it from sleep mode. If the wake event was power button  130  being pressed, the ASI processor  210  performs step  523  enabling host processor  410  into its operational mode. In operational mode, host processor  410  is powered on to perform the main operations of the host system. For example, when the host system is AED  100 , the main operations comprise patient heart rhythm analysis and possible delivery of defibrillation shocks to the patient. After enabling the host processor  410  into operational mode, ASI processor  210  may continue its operation according to the method  500  in parallel to operational functions of the host processor  410 . However, host processor  410 , while in its operational mode, may preempt use of indicators  420  or sensors  430  for operational functions. As examples, while in operational mode, host processor  410  may use speaker  160  to provide instructions to the operator, or microphone  340  to record audio of the rescue attempt. 
   During step  523 , the host processor  410  may also query the ASI processor  210  for the environmental conditions of the AED  100  that are sensed by the ASI processor  210 . The host processor  410  can use these environmental conditions sensed by the ASI processor  210  to adjust intensity level, duration of powering, or duration between powering of its operational indicators such as a speaker  160  or a LED  235 . 
   If the wake event determined in step  520  is a test event, ASI processor  210  transitions to step  526  where internal self tests are initiated by ASI processor  210  and performed by ASI processor  210 , host processor  410 , or other system circuitry. A test event may be caused by a periodic test timer, a user request, or an external event such as the insertion of a new battery. Once self tests are completed, ASI processor  210  transitions from testing step  526  into step  580  where ASI processor  210  returns to sleep mode of step  510 . 
   If the wake event determined in step  520  is an indicator timer, ASI processor  210  transitions to decision step  529  where it is determined if the ambient environment should be sensed on this timer cycle. In a preferred, yet exemplary embodiment, the ambient environment is sensed less frequently than the indicator is powered. That is, the inventive ASI system may not detect environmental conditions every time a status indicating event is scheduled to occur. The inventive ASI system can detect environmental conditions such as ambient light conditions or ambient acoustic noise conditions at a rate that can be different than the frequency set for an indicating event. That is, the environment may be sensed more or less frequently than the indicator is powered. One of ordinary skill in the art will appreciate that such alternate embodiments of the inventive method do not depart from the spirit or scope of the invention. 
   If it is determined during decision step  529  that the ambient environment is to be sensed, ASI processor  210  transitions to routine  530  where the ambient environment is sensed and then to routine  540  where the intensity, duration, and frequency of indicators are set according to ambient conditions sensed in routine  530 . Further details of routines  530  and  540  will be discussed below with respect to  FIGS. 6 and 7 . If it is determined during decision step  529  instead that the ambient environment is not to be sensed during this timer cycle, the ASI processor  210  transitions directly to step  550 . 
   In decision step  550 , ASI processor  210  determines if an indicator event should be performed during the current indicator timer cycle or not. This feature allows the ASI system to slow down the rate of indicator events by skipping indicator cycles. One of ordinary skill in the art will appreciate that this same effect may be achieved by modifying the duration of the indicator timer used to wake the ASI processor  210  from sleep mode  510  into step  530 . If no indicator event is to be performed during a specific cycle, ASI processor  210  transitions from decision step  550  into step  580  where ASI processor  210  returns to sleep mode of step  510 . 
   In step  560 , ASI processor  210  performs the indicator event. This indication may comprise flashing LED  235 , or sounding speaker  160 , or some other type of active status indication. 
   In step  570 , ASI processor  210  may analyze indicator reflections to determine if the host system is currently enclosed. Using light sensor  240  to measure the proportion of light emitted by indicator  235  that is reflected directly back into the host system, the ASI processor may determine that there is an enclosure or cover surface immediately outside the host system housing  110 . ASI processor  210  may respond to the presence of this surface as an indication that the host system is enclosed and therefore slow or cease visual status indication. Similarly, reflections or echoes of an aural indicator, such as speaker  160 , may be detected using microphone  340 . These echoes may likewise indicate the presence of an enclosure or cover surface outside the host system. 
   After step  570 , the ASI processor  210  returns to its sleep mode in step  580  in which the host device is in a non-operative state. As noted previously, a non-operative state of the host device usually includes situations in which the host device is performing less than all of its primary functions. For example, a non-operative state for automatic external defibrillators (AEDs) usually includes situations in which an AED is not performing a rescue on a patient. Functions that may occur during non-operative states in AEDs may include self-tests and active status indicator events performed by ASI processor  210 . 
   Referring now to  FIG. 6A , a logical flow diagram of routine  530  illustrates the process of sensing ambient environment in an environmentally responsive ASI system with visual indication. In step  610 , ASI processor  210  samples photodiode light sensor  240 . In step  620 , ASI processor  210  stores a measure of the ambient light intensity, or brightness, around the host system using the sampled data from step  610 . This stored measure is used later in routine  540 . Finally, in step  690 , the routine  530  returns to the main process  500  illustrated in  FIG. 5 . 
   Referring now to  FIG. 6B , a logical flow diagram of routine  530  is illustrated for sensing the ambient environment in an environmentally responsive ASI system with aural indication. In step  650 , ASI processor  210  samples microphone  340 . In step  660 , ASI processor  210  stores a measure of the ambient sound intensity, or loudness, around the host system using the sampled data from step  650 . This stored measure is used later in routine  540 . Finally, in step  690 , the routine  530  returns to the main process  500  illustrated in  FIG. 5 . 
   Referring now to  FIG. 7A , a logical flow diagram of routine  540  is illustrated for setting indicator intensity and frequency in an environmentally responsive ASI system with visual indication  235 . In step  710 , ASI processor  210  retrieves the stored measure of ambient light intensity from the stored value that was calculated by routine  530 . In step  720 , ASI processor  210  sets the intensity to be used when flashing the light indicator  235 . This setting is made based on the ambient light intensity retrieved in step  710 . For example, if the ambient lighting is dim, the ASI processor  210  may set the indicator light  235  intensity to a lower level or if ambient lighting is bright, ASI processor may set indicator light  235  intensity to a higher level. 
   In addition to these two relative examples of higher and lower light intensities, there may be many levels of intensity available to be set according to many different ambient brightness levels that may be sensed. Indicator brightness levels may be computed from the measured ambient light intensities, or alternatively, value ranges stored in one or more tables present in memory may be used to map measured ambient light intensities to appropriate indicator brightness levels. In step  725 , ASI processor  210  sets the duration for powering indicator light  235  to create a flash. In step  730 , ASI processor  210  sets the delay between illuminations of the indicator light  235 . This feature may save battery power  220  by slowing the flashing of the indicator light  235 . Finally, in step  790 , the routine  540  returns to the main process  500  illustrated in  FIG. 5 . 
   Referring now to  FIG. 7B , a logical flow diagram of routine  540  is illustrated for setting indicator intensity and frequency in an environmentally responsive ASI system with aural indication via speaker  160 . In step  750 , ASI processor  210  retrieves the stored measure of ambient sound intensity from the stored value that was calculated by routine  530 . In step  760 , ASI processor  210  sets the intensity, or volume, to be used when sounding speaker  160  as a status indicator. This setting is made based on the ambient sound intensity retrieved in step  750 . For example, if the ambient sound level is high, the ASI processor  210  may set the volume of speaker  160  to a higher level so that it can be heard over the ambient noise. 
   If the ambient noise level is low, the ASI processor  210  may set the volume of speaker  160  to a lower level. In addition to these two relative examples of higher and lower speaker volume, there may be many levels of volume available to be set according to many different ambient noise levels that may be sensed. Speaker volume levels may be computed from the measured ambient noise intensities, or alternatively, value ranges stored in one or more tables present in memory may be used to map measured ambient noise levels to appropriate speaker volume levels. In step  765 , ASI processor sets the duration for sounding speaker  160  during a speaker chirp. In step  770 , ASI processor sets the delay between soundings of speaker  160 . This feature may save battery power  220  by reducing the amount of energy used in sounding speaker  160  over a given period of time. Finally, in step  790 , the routine  540  returns to the main process  500  illustrated in  FIG. 5 . In addition to the functionally of routine  540  setting the volume of speaker  160  for status indication purposes, the host processor  410  may retain these volume settings for speaker  160  during operational mode where it may use speaker  160  to provide instructions or other audio to the operator. 
   Referring now to  FIG. 8  which is an elevation view illustrating surface-mounted LED  235  and surface-mounted photodiode  240  both optically coupled to the same light pipe  140  according to one exemplary embodiment of the invention. Host system housing  110  encloses a light pipe  140  for optically coupling both LED  235  and photodiode  240  to the outside of the system housing  110 . However, in other exemplary embodiments (not illustrated), the LED  235  and photodiode  240  may have separate light pipes  140  for propagating light into and out of the host system housing  110 . 
   Light emitted from LED  235  is directed out through the outside surface  810  of the light pipe. Ambient light conditions outside the host system housing  110  may be directed from outside surface  810  of light pipe  140  into photodiode  240 . 
   Both LED  235  and photodiode  240  are surface mounted to printed circuit board  830  where they are in electrical communication with ASI processor  210 . Light pipe  140  may simplify system manufacture by enabling the use of surface mount components  235  and  240 . An additional benefit of light pipe  140  may detect reflections off of surfaces beyond light pipe surface  810 . ASI processor  210  may respond to the presence of these surfaces as an indication that the host system is enclosed and therefore slow or cease visual status indication. 
   Alternative embodiments of the environmentally responsive ASI system will become apparent to one of ordinary skill in the art to which the present invention pertains without departing from its spirit and scope. Thus, although this invention has been described in exemplary form with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts or steps may be resorted to without departing from the spirit or scope of the invention. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description.