Reverse engineered circuit diagram of a popular retail doorknob alarm. It contains a small transmitter and the doorknob acts as an antenna so it will not work on a metal door. When a person comes close to the doorknob this loads down the oscillator and the alarm sounds. The proximity sensor circuitry is perfectly capable of driving 74HCT series CMOS logic in place of of the sound effect IC's shown in the circuit diagram.
I do not gaurantee the accuracy or safety of any information herein.
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