but it can be used for a wide variety of purposes for example you can connect the IC pin2 with the door locks, bicycle locks etc. so it will beep when someone touches the lock.
This circuit will give you a beep of few seconds when someone touches the metal but you can increase the beep time to 2 to 5 minutes by increasing the value of the capacitor Cx. A 100uF electrolytic capacitor will give you a beep of around 2 minutes this time period can be further increased to 5 minutes by increasing the value from 100uF to 220uF. A 1K variable resistor is used between the pin three and buzzer to control the volume of the buzzer.
You can also remove the 470 Ohms resistor and LED for making the circuit more simple. You can fit the whole circuit in a very small box with the two or four small coin size lithium batteries.










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Here is a very interesting project / schematic of a touch alarm circuit using a 555 timer IC. The circuit is quite sensitive and it will activate a peizo or any other buzzer and an LED for a set time period when any one touches the metal plate attached with the pin 2 of the IC NE555.
The circuit is very simple




 
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Touch Alarm Circuit Schematic