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Sensors are the most vital part of the system; they act like the eyes and ears of a home alarm system by monitoring break in points and interior areas. The typical sensors
, which are usually two magnets, are generally installed on doors and windows such that one magnet is connected to the door or window and the other is connected to the door or window frame. When the door or window is opened, one magnet is removed from the surrounding area of the other and the sensor registers that the door has been opened. More advanced home alarm systems may also contain vibration sensors to detect when glass has been broken by measuring the vibrations caused by the breakage. Also, many systems use motion sensors that compute the proximity of a room’s walls by producing infrared
beams and measuring the time required for them to bounce back; if a beam comes back sooner than expected, it likely bounced off of a person and the sensor registers motion. The control center keeps track of the status of the sensors and reports activity through LCD displays and other output devices. Moreover, when activity takes places, such as the opening of a window, the sensors report the activity to the control center and the center registers that a disturbance has occurred. In managed alarm systems, the control panel also checks the sensors to verify that they are still operational; if a sensor fails to reply, the center alerts the home owner of an out of order sensor. If the home owner activates the alarm system and the control center registers activity in the home, a signal is sent by the control to a buzzer, flashing lights or any other audiovisual alarm element. Our design for a functional keypad was the usage of an alternation of ports between inputs and outputs which is done by using the TRIS function. We started off by setting the first four ports of PORTB as the inputs and the latter four ports as the outputs.