Assistive listening devices are used to maximize hearing using instruments which may or may not be used in conjunction with a hearing aid. These instruments fall into several categories:

1. Telephone Amplifiers.
2. Infrared Listening Systems for Television and Theater.
3. FM Listening Systems for lectures, conversation in noisy places, or at business meetings.
4. Devices to Warn of Fire.
5. Signalling Devices Such as Doorbells and Telephone Ringers.
6. Terminals to Communicate over Telephones.