Car Antitheft wireless Alarm
This anti-theft alarm FM radio-control can be used with any vehicle having 6 - with the power supply 12 volt DC. The mini VHF, FM transmitter is installed in the vehicle at night when parked in the car porch or car park. CXA1019 receiver with a single module IC-based FM radio, which is freely available on the market at reasonable prices, remains inside. The receiver is tuned to the frequency of the transmitter. When the transmitter is on and the signals are being received by FM radio receiver, no hissing is available at the output of the receiver. Thus transistor T2 (BC548) does not hold. This results in the driver transistor T3 getting its relay forward base bias via 10k resistor R5 and the relay is energized. When an intruder tries to drive the car and takes a few meters from the driveway, the radio link between the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hiss. Hissing AC signals are coupled to relay switching circ-uit via audio transformer. These AC signals are rectified and filtered by diode D1 and C8 capacitor and the resulting positive DC voltage provides a forward bias of transistor T2. Thus transistor T2 conducts, and pull the base of relay driver transistor T3 to ground level. The relay which disables the alarm connected via N / C relay is on. If, by chance, the intruder learns the wireless alarm transmitter and disconnect the battery, the alarm is still remote, because in the absence of the signal, the receiver continues to produce hissing noise at its output. So the burglar alarm is foolproof and reliable.