Listening devices can help evaluate threats and safety levels of people in many situations. A wireless microphone or wireless listening device broadcasts surveillance conversations to a radio receiver or communications receiver. These are the most common:

Concealable transmitters

These can monitor conversations in a room if gaining access is difficult, by using room transmitters, body wires, wireless microphones or similar. These listening devices are self contained, free-standing, and can be placed in a room where discovery would be unlikely yet close to where conversations take place.

Disguised transmitters

These are covert transmitters are used for covert surveillance by placing audio transmitters into everyday objects such as a clock, belt, calculator, ashtray, the user conducts undercover operations, with customised housings for the transmitter.

Digital surveillance transmitters

These are listening devices with features such as remote controlled activation, audio surveillance recorder features, encrypted surveillance transmitters, and data monitoring transmitters.

Listening devices

Listening devices that transmit audio surveillance over long distance while drawing very low power output are known as lithium transmitters. These listening devices are very small and can be placed in hard to view areas.

Telephone transmitters

These are listening devices used for phone tapping in order to obtain both sides of a phone conversation. These listening devices are telephone wiretaps that live off the energy of the phone line, prolonging their operation life indefinitely.

Mains powered transmitters

These are listening devices and broadcast audio surveillance for extended use where continuous power exists, and audio surveillance access is difficult to get. These listening devices can operate indefinitely due to the AC power line that provides continuous power to the listening device.