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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
   Restrooms can be breeding grounds for disease-spreading bacteria. As a result, there is a growing desire to develop systems for restrooms that eliminate human contact with restroom surfaces. Additionally, water conservation concerns have created a desire to control water usage by preventing excessive flushing. 
   Many present toilets and urinals are operated by a manual flush handle. The user operates the toilet or urinal by displacing the position of the flush handle. The manual flush handle controls the flow of water into the toilet or urinal device. Manual flush handles present several problems. The problems may include a reluctance to touch the flush handle due to possible bacteria. As a result, the toilet or urinal may remain unflushed, leaving waste in the toilet or urinal, creating the unsanitary conditions. 
   In addition, a user can often hold the manual flush handle in an open position for an excessive time period. Maintaining the handle in an open position may waste water, and lead to additional costs or flooding. As a result, devices for automatically controlling the flushing of toilets or urinals have been developed. 
   These devices may include sensors to detect the presence of a user. The device may then flush the toilet or urinal when the sensor no longer detects the presence of the user. When these sensors are directly attached to devices; they are exposed to possible vandalism or theft. Vandalism or theft reduces the cleanliness of the restroom and creates extra expense to repair or replace the device. 
   BRIEF SUMMARY 
   The present embodiment relates to in-wall sensor assemblies. The in-wall sensor assembly includes a housing with a circular flange, coupled to a side wall. The circular flange extends beyond the outer surface of the side wall. The in-wall sensor assembly also includes a fastener proximate to the outer surface of the side wall and a sensor located within the housing. The in-wall sensor assembly may also include a face plate removably attached to the housing and a power source coupled to the housing and the sensor. 
   A method for installing an in-wall sensor is also disclosed. The method includes inserting a housing into a hole in the wall. The housing may have a circular flange having a diameter larger than the diameter of the hole and a side wall attached to the circular flange. The side wall has a diameter that fits in the hole in the wall. The housing also includes a fastener attached to the outer surface of the side wall, and coupled to a tab. When the fastener is drawn towards the flange, the tabs move to a position substantially perpendicular to the housing and against an inner surface of the wall, locking the housing into place. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an embodiment. 
       FIG. 2  is an exploded view of an embodiment. 
       FIG. 3  is a perspective view of the front of the housing. 
       FIG. 4  is a perspective view of the rear of the housing. 
       FIG. 5  is a perspective view of the front of the cover plate. 
       FIG. 6  is a perspective view of the rear of the cover plate. 
       FIG. 7  is a side view of the key. 
       FIG. 8  is a perspective view of the housing showing the fastener. 
       FIG. 9  is a perspective view of the retaining tab. 
       FIG. 10  is a perspective view of the battery pack. 
       FIG. 11  is an exploded view of battery pack and the sensor. 
       FIG. 12  is a perspective view of the sensor attached to a non-tank-style toilet. 
       FIG. 13  is a cut-away perspective of an automatic flush valve apparatus. 
       FIG. 14  is a perspective view of the sensor wired to a non-tank style valve. 
       FIG. 15  is a perspective view of the sensor and a tank style valve. 
   

   DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  present a generalized view of an in-wall sensor assembly. The assembly includes a housing  100 , a removable face plate  110 , and a removable key  130 . The face plate  110  has a window  120  through which a sensor can function. The assembly further includes a power source  220  and a sensor element  210 . 
   The housing  100  is shown in detail in  FIGS. 3 and 4 . The housing includes a body  310  having an open end  330  and a circular flange  320 . As shown, the flange  320  has a diameter larger than the body  310 . The housing  100  may be made of any sturdy material, but is preferably made of plastic or metal. In one embodiment, the housing  100  has a hole  340  in the end opposite the flange  320  to accommodate wires for electrical connections. However, the hole  340  may be placed anywhere in the housing. The inside of the housing may be generally square shaped, with two flat walls  360  parallel to each other, and the other two walls having a curved portion  370  and a flat portion  380 . A hole  350  may be concentrically located within the curved portion  370 . Additionally, the housing may contain threads  390  near the open end  330 . 
   The body  310  may have any shape, including cylindrical, octagonal, or cubical. As shown in  FIG. 4 , the housing may be generally cubical, having two flat outside walls  410  parallel to each other. The other two side walls may have flat portions  420  and curved portions  430 . Channels  440  may be disposed between the flat portions  420  and the curved portions  430 . On one side of the channels  44 , ridges  450  may be present. The channels may run the length of the body and terminate at the holes  350  ( FIG. 3 ) near the front of the housing. 
   A face plate  110  is shown in  FIGS. 5 and 6 . The face plate may be disk-shaped, with a circular opening  510  in the center. In one embodiment, a window  120  may be positioned within the circular opening  510 . Two indentations or openings  520  may be positioned in the outer surface of the face plate  110  to assist in the attachment of the face plate  110  to the housing  100  ( FIG. 1 ). The inside of the face plate is depicted in  FIG. 6 . The face plate may have an inner ridge  610  contains threading on the outside, which matches the threaded portion  390  ( FIG. 3 ) of the body. The face plate may be made from a durable material, preferably metal, most preferably stainless steel. 
   The face plate  110  ( FIG. 1 ) may be secured to the body  100  through the use of a key  130  ( FIG. 1 ), which is shown in  FIG. 7 . The key has a handle  710  and two projections  720 . The projections  720  match up with the indentations  520  ( FIG. 5 ) of the face plate  110 . 
   As shown in  FIG. 8 , screws  810  may be positioned in the channels  440  ( FIG. 4 ) of the housing  100  ( FIG. 1 ). The heads  820  of the screws  810  are located in the holes  350  ( FIG. 3 ). A tab  830  contains threading that corresponds to the threading of the screw  810 . Therefore, the tab  830  may be threaded onto the screw  810 . 
     FIG. 9  depicts the tab  830 . The tab may include a cylindrical channel  910  that is threaded to fit around a screw  810  ( FIG. 8 ). Attached to the cylindrical channel  910  is a flap  920 . The tab may be made of durable material including, but not limited to metal, plastic, or a composite material. 
   Within the housing  100  ( FIG. 1 ) is a power source  220  ( FIG. 2 ), which is depicted in  FIG. 10 . The power source may be a battery pack  1000  to hold one or more replaceable batteries, which would be located within the battery pack  1000 . The battery pack  1000  may have one or more chambers  1010  to hold one or more batteries. The battery pack  1000  may be modified for different sizes and numbers of batteries. The present battery pack  1000  has four chambers  1010  to hold four batteries of a type, preferably AA or C size 1.5 volt batteries. Each chamber  1010  may have one or more clasps  1020  to help secure the battery in place. At one end  1030  of the battery pack  1000 , a plurality of holes  1040  may be present to allow physical attachment of the sensing means to the battery pack. An additional opening  1050  may be present to allow an electrical connection between the sensor and the power source. 
   As depicted in  FIG. 11 , a printed circuit board (PCB)  1110  may be connected to the battery pack  1000 . The PCB  1110  contains the electronic circuitry necessary to operate the sensor. The PCB  1110  may be electrically connected to the power source and to a sensor block  1120 . The PCB  1110  may be protected by the PCB cover  1130 . The PCB cover  1130  may have an opening  1140  in the center to allow for placement of the sensor block  1120 . The PCB cover  1130  may be secured to the battery pack  1000  by at least one fastener, such as a screw, through PCB cover holes  1150  and PCB holes  1160 . The sensor block  1120  may be connected to the PCB  1110  and contains sensing element which senses the presence of an object or occurrence at some distance from the sensor. The sensor may be based on motion, infra-red, body heat, or any basis that converts non-electrical energy into electrical or optical energy. 
   During insertion of the housing  100  ( FIG. 1 ) into the wall, the tabs  830  are positioned parallel to the housing body  310  ( FIG. 3 ) adjacent to the flat portion  420  ( FIG. 4 ). After insertion of the housing  100  ( FIG. 1 ) into the wall, the screws  810  are tightened. The turning rotates the tabs  830  into a position generally perpendicular to the housing body  310  ( FIG. 3 ). Ridges  450  ( FIG. 4 ) keeps the tabs  830  in a perpendicular position. Additional turning of the screws  810  forces the tabs  830  towards the flange  320  ( FIG. 3 ). Eventually, the assembly is secured to the wall by the wall being snuggly located between the flange  320  ( FIG. 3 ) and the tabs  830 . 
   Once the housing is securely situated in the wall, the power source  220  ( FIG. 2 ), which may include batteries, as well as the sensor and PCB  1110  ( FIG. 11 ) may be situated inside the housing. Furthermore, the face plate  130  ( FIG. 1 ) may be attached to the housing  100  ( FIG. 1 ) by placing the projections  720  ( FIG. 7 ) of the key  130  ( FIG. 1 ) into the indentations  520  ( FIG. 5 ) of the face plate  110  ( FIG. 1 ) and turning the key  130  ( FIG. 1 ) in a clockwise direction, thereby turning the face plate  110  ( FIG. 1 ) engaging the threading  390  ( FIG. 3 ) of the housing and the threading  620  ( FIG. 6 ) of the face plate. Once the face plate  110  ( FIG. 1 ) is secured on the housing  100  ( FIG. 1 ), the key  130  ( FIG. 1 ) can be removed from the face plate  110  ( FIG. 1 ), making the face plate  110  ( FIG. 1 ) difficult to remove. The face plate may be removed from the housing  100  ( FIG. 1 ) by again inserting the projections  720  ( FIG. 7 ) of the key  130  ( FIG. 1 ) into the indentations  520  ( FIG. 5 ) and turning the key  130  ( FIG. 1 ) and face plate  110  ( FIG. 1 ) in a counter-clockwise direction. Turning the face plate  110  ( FIG. 1 ) in a counter-clockwise direction will disengage the threading  620  ( FIG. 6 ) of the faceplate  110  ( FIG. 1 ) from the threading  390  ( FIG. 3 ) of the housing  100  ( FIG. 1 ). 
   The in wall sensor may be used for controlling the flush valve on a urinal or toilet, including both tank and non-tank style toilets. When used in tandem with a flush valve, the in wall sensor may send an electrical signal through an electrical connection a wireless electromagnetic signal, such as an infrared signal, to the flush valve. In operation, the sensor detects the presence of a user or a specified condition and sends an activation signal to the sensing logic or electronics mounted on the printed circuit board in the housing. Alternatively, the sensor may provide an activation signal when a user departs from a field of view, when a light is turned on, after an elapsed time period, or some other condition. 
   As shown in  FIG. 12 , an in-wall sensor unit may electronically connect to the flush valve of a non-tank style toilet. The electrical connection may be a wire  1210 . The wire  1210  may run out of the back of the housing  100  ( FIG. 1 ), behind the wall, and out of the wall through an escutcheon  1220  to connect to the flush valve actuation apparatus. The flush handle actuation apparatus may include a modular housing unit  1230 . The housing unit  1230  is adapted to be easily mounted to flushing mechanism housing  1240 . 
   The mechanics of the actuation device are shown in  FIG. 13 . A modular housing unit  1310  may contain a motor  1320 , which may be mounted to the housing unit  1310 . The motor  1320  may be mechanically connected through a reduction gear train  1330  to an actuating element  1340  which is mounted on a gear  1350  of reduction gear train  1330 . As motor  1320  is activated, reduction gear train  1330  partially rotates gear  1350  in a counter-clockwise direction. Therefore, actuating element  1340  moves to the right, pushing against plunger pin  1370 . Plunger pin  1370  then moves against the stem of the valve  1380 . As the stem  1380  tilts, it activates the flushing mechanism (not shown). The motor  1320  is then deactivated, and a spring  1360  forces the actuating element  1340  and gear back to their original position. 
   Alternatively, the in-wall sensor may send a signal to the flush valve by means of an electromagnetic signal, as depicted in  FIG. 14 . When the sensor assembly  1410  detects the presence of a user or a specified condition, a transmitter (not shown) in the in-wall sensor assembly  1410  sends an activation signal to a receiver (not shown) in the flushing mechanism housing  1420 . The receiver then activates an actuation device, similar to the one depicted in  FIG. 13 , which then activates the flushing mechanism. 
   The in wall sensor can also operate with a flush valve for a tank style toilet. The in wall sensor sends a signal, either through an electrical connection or a wireless signal, to the flush valve. As illustrated in  FIG. 15 , the automatic flushing actuator for tank style toilets may include a housing  1510  and a mounting clamp  1520 , which are adapted to be placed inside the tank of a toilet and secured to the overflow pipe (not shown). The housing  1510  comprises a lower portion or base  1530  and an upper portion or cover  1540  having a dual part lever assembly  1550  mounted thereon. Activation of a motor (not shown) occurs when the sensor assembly (not shown) transmits an electrical signal or an electromagnetic signal to a receiver in a circuit board (not shown) in the housing. The motor in turn activates a gear reduction mechanism (not shown) and causes gears and a cam (not shown) mounted thereon to rotate. The gear having the cam mounted thereon rotates through one complete revolution for each flush cycle. As a result of activation, the cam pushes an actuator rod  1560  in an upward direction. The actuator rod  1560  then pushes on a lever  1570  causing lever  1570  to rise in an upward direction. As the lever  1570  is raised, a chain (not shown) attached to the lever  1570  is placed under tension causing the valve flap lid (not shown) to be lifted off of the flush valve (not shown), thereby flushing the toilet. 
   Various embodiments of the invention have been described and illustrated. However, the description and illustrations are by way of example only. Other embodiments and implementations are possible within the scope of this invention and will be apparent to those of ordinary skill in the art. Therefore, the invention is not limited to the specific details, representative embodiments, and illustrated examples in this description. Accordingly, the invention is not to be restricted except as necessitated by the accompanying claims and their equivalents.

Summary:
A sensor assembly which is located within a wall is disclosed. The sensor assembly is typically attached to a unit for automatically flushing a toilet or urinal. The sensor assembly includes a housing, a flange, a fastening means, a face plate, a power source, and a sensor. The housing is located in a hole in a wall and fastened by flange and fastening means. The housing will hold the power source and the sensor, which will be enclosed by the face plate. A key which fits in indentations in the face plate and is used to attach and remove the face plate is disclosed. Finally, a method of installing the sensor assembly is disclosed.