Tracking Systems One of the most useful but often overlooked tactics for the amateur spy involves tracking devices of various sorts, and it’s much cheaper than hiring a private investigator. Older devices and more traditional tracking devices included “bumper beepers.”
These are small devices that can be placed under or inside the car bumper belonging to your tracking target. They are only a few inches long and wide, and attach to the bumper with strong magnets or double-sided adhesive. Their function is to assist you in following a vehicle that is under your watch. They are radio transmitters that will give you certain information regarding the bearing and relative speed of the vehicle being tracked.
These things are pricey too, $400 or so at the low end, and the more expensive units will be able to give more information with regard to the specific location of the vehicle.
A familiar tool for private detectives, bumper beepers give you an idea of how close to stay to the vehicle to avoid losing it, and how far away to stay to avoid detection.
One benefit of this method is that since antisurveillance legislation is focused mainly at the act of intercepting verbal or textual communications, laws in most places do not account for bumper beepers. They do, however, require a degree of know-how to be used effectively.
More importantly, digital technology and global positioning systems (GPS) make this a more or less obsolete option.