One of the simplest devices is a detector for hidden wiring, is presented in Fig. 1. The resistor R1 is needed to protect the IC CLA from high voltage static electricity, but, as practice has shown, it can not be put. Antenna is a piece of ordinary copper wire of any thickness. The main thing is that it does not bend under its own weight, i.e. was quite hard. The length of the antenna determines the sensitivity of the device. The most optimal value is 5...15 see When approaching the antenna to the wiring detector produces a characteristic crackling.
Such a device is very convenient to determine the location of the burned out lamp in a Christmas garland - near the crackling stops. System type SN-3 is included in a bridge circuit that provides increased volume "cod". In Fig.2 shows a more complex detector having, in addition to audio. and light indication. The resistance of the resistor R1 should not be less than 50 megohms.
In the circuit VD1 led current-limiting resistor no. since DD1 chip (CLA) with this function copes well itself.
If the input currents of the element D1.1 let us, then removing the resistor R1 from the circuit depicted in Fig.2, we get a device that reacts to a change in static potential in the surrounding space. For this antenna WA1 do with the length of 50...100 cm using any wire. Now the device will react to the movement of the human body. Putting such a device in a bag, get a standalone security device, outstanding light and sound signals if the bag or around it happen any manipulation.
Publication: N. Bolshakov, rf.atnn.ru