How to Make a Sensor Alarm

Detach the back of a Radio Shack motion-sensing alarm and disconnect the wires to the siren.

Solder a new pair of wires to the siren wires in the motion detector. They should be long enough to stretch between the point where you want to mount the motion sensor and the point where you want to place the keypad. Mark one of the wires as a ground wire by wrapping a piece of tape around it or running a felt pen over the insulation.

Thread the new wires through the battery case and reassemble the motion detector. The siren can now be controlled by the remainder of your system.

Connect a 4x4 keypad to its proper controller and attach the wires to a CB280 study board. The black wire should be attached to the GND port, the red wire to the 5v port, and the remaining four pins to ports P0, P1, P2 and P3.

Attach an CLCD420-B LED read-out to the CuNET connection on the study board.

Connect the ground wire of the sensor to the GND of the study board, and the other wire to the center of a 2N3904 transistor.

Connect the 5v of the study board to the left side of the transistor and the P21 port of the study board to the left side of the transistor.

Connect the output on the LED to the P21 port of the study board. That should enable the motion sensor.

Set the sensor to "chime" and wiggle your fingers across the front. The LED should detect it.

Unzip the programming from the URL below and download it into the study board.

Set the password on your key pad: usually a sequence of four numbers. The next time you type in those numbers, the LED light will activate, indicating that the alarm is live.

Mount the motion detector in a corner or somewhere that provides maximum exposure to the space you want to protect. Mount the remaining components somewhere easily accessible nearby.