The brightness of the indicator LED and the pitch of the audible tone will increase proportionally with the strength of the detected signal, making it simple and easy to locate the interference source. One of the typical applications of the ERD-1500 is to locate sources of electromagnetic interference. Light dimmers are known sources of interference, owing to their use of solid-state switching circuits.
Some brands are worse offenders than others.
A faulty dimmer such as the one shown here may turn into a wide-band interference generator causing considerable degradation of radio and TV reception. The sales of bugging devices are booming and there is overwhelming evidence of their wide-spread use. Surveillance countermeasures is yet another important application of this unit. In the pictured situation, a radio surveillance device is hidden in a house intercom. Miniature transmitting devices may be hidden in many objects of daily use.