This is door knob touch alarm for your home security purpose. The alarm will be activated when someone touch the metal door knob. This circuit won’t work on full metal door.
The supply power for this door touch alarm is 3V DC, two AA batteries can be used to operate this circuit to make this circuit portable. Since this circuit consumes very small power, the battery will be last very long. A variable resistor used to adjust the sensitivity of the touch.
Please read above schematic diagram and some notes on the image diagram first before assemble this circuit.
Download the schematic drawing