If you want to protect your car from burglar, the following car wireless burglar alarm would be suitable for your needs. It can be used for any car who has 6V or 12V DC supply system. The mini Very High Frequency FM Transmitter is placed in the vehicle.
A single FM radio module which is used as a unit receiver is CXA1019, an affordable integrated circuit. Receiver is tuned to the transmitter’s frequency at the output receiver no hissing noise is available when the transmitter is on and the signal being received by FM radio. This will make the transistor T2 (BC548) does not conduct. Thus the relay driver resistor T3 getting its forward bias through resistor R5 and the relay gets energized.
How is the alarm working? Whenever the radio link between the car (transmitter) and the alarm (receiver) is broken, it will sound the alarm. The FM radio modules generates hissing noise. Hissing AC signal are coupled to relay switching circuit through audio transformer. These AC signals are filtered and rectified by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2. This transistor pulls the base of the relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on.
What if by chance the intruder finds out the wireless alarm and disconnect the transmitter from battery? Do not be worry, the alarm will still be activated because in the absence of signal, the receiver continues to produce hissing noise at its output. Therefore this alarm is fool-proof and highly reliable.