The most effective means of tailing a vehicle is with a bumper
beeper. An electronic tailing device, the bumper beeper
attaches to the underside of the victims car. The device sends
beeping signals to a receiver in the tailing vehicle. The closer
the tailing vehicle gets to the target vehicle, the louder the
beeps become. The more sophisticated beepers are equipped with
a null switch, whereby a different tone in the beep is produced
if the victim turns right or left. Bumper beepers have an
effective range of 2 to 12 km (1 to 5 miles). They are usually
attached to the vehicle with powerful magnets, although heavy
metal clamps are sometimes used. Beepers can be either battery
powered or attached directly to the target vehicle's own
electrical system.
DETECTION OF BUMPER BEEPERS
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To determine if you are the victim of these dreaded devices,
first make a complete visual inspection of the underside of
your vehicle. What you are looking for is a small metal box
with one or two skinny antennas sticking out of it.
If your search turns up nothing, go out and buy a field
strength meter (Radio Shack # 25-525). These devices detect
all radio transmissions. With meter in hand and car ignition on,
check in, on, and especially under your car. If you are a
victim of a bumper beeper you will find it.