Electronic tagging is a method of monitoring the whereabouts of a person, such as in the enforcement of house arrest. The person sentenced to house arrest is tagged with a plastic anklet or bracelet. The tag contains a tiny radio transmitter, which continuously sends a signal to a receiver connected to the telephone network. The receiver detects the signal only when the tag is within a certain distance, for example, inside or close to the house where the person is detained. A central monitoring unit dials the receiver at random intervals and checks whether the radio signal from the tag is still being received.