Radiation signals from electrical wiring can travel a few meters away. These can be induced by the electromagnetic field in the human body as well. This tactile alarm is based on the generation of the AC buzzer signal. When someone touches the touch plate, a low-power AC hum (the same one that is induced from the house's AC wiring) is generated on the touch plate. This signal is first amplified by the high gain preamplifier built around IC 741 (IC1) and then fed to another operational amplifier CA3140 (IC2) which is wired as a voltage comparator.
When IC2 receives the amplified signal on its input pin 3, its output is high. As a result, the transistor T1 leads to sound the buzzer. At the same time, LED1 illuminates. For satisfactory operation of this unit, connect it from the 12V network.
Mount the circuit in a general purpose PCB and lock in a small cabinet. Use a shielded cable to connect the touch plate to the circuit keeping the length of the cable and the size of the touch panel as short as possible.