This is a phone bug circuit. This wireless telephone line spy circuit can be used to transmit the phone conversation to a nearby FM radio. This circuit must connected to a normal phone line. Here is the schematic diagram of the circuit:
The first transistor is turned off, if the voltage drops to less than 15v (if the telephone line is in use). It will enable the second transistor to oscillate at approx 100MHz. Then transmit the phone conversation to a nearby FM radio.