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Monday, September 28, 2009

Touch Door Alarm Circuit Using 555 Timer IC

This is a design simple alarm that can be used to provide a audible alarm when someone touches the door knob or handle of your room. The door knob or handle must be made of metal for the circuit to work. The main chip in the circuit is a 555 timer which will be triggered if a hand comes close to or touches the door knob.

The circuit attaches to the door knob at the end of the 1 Mega ohm resistor. This is operation of the circuit. Once the timer is triggered the LED will light and the UJT will output a tone to the speaker. The timers will time out in 5 seconds. The sensitivity of the trigger can be changed by changing the 1 Mega ohm resistor to another value. The 5 second time out can be adjusted by changing the value of the resistor connected between pin 8 and pin 7. The output tone can be changed by changing the RC values on the base of the UJT.


  1. Thank You Nice Circuit......

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  2. I want such a circut in which it triggre a alarm on applying pressure on a pressure sencitive plate. It should trigger 3 alarm simul. and the 1st alarm should produce sound for 3 sec. and then the next 3 sec. the second should be triggered and for the final 3 sec. the third should be triggered also the alarm should stop if the pressure is being applyied for more than 9 sec.