Also, may be wired directly to a listening post. Bumper Beeper - A radio transmitter which is attached to a vehicle for use as a beacon or homing device for tailing. The signal travels along the wires with very little radiated from the lines. An impressive array of electronic equipment is available for use in invading your privacy.
Most toy stores carry inexpensive walkie-talkies that are ideal for a quick and dirty room bug.
The eavesdropper simply installs the battery, tapes down the transmit button and hides the walkie-talkie in the target room. Not only can mom use it to keep an ear on her little one, but since it has a transmit range of about three blocks, it makes a nifty bug also. One of the most common telephone bugging attacks is the hookswitch bypass. This means that even though the phone is hung up, it intercepts all room conversation and passes them down the phone line to a listening post. About 45 cents.