Most wireless intercom systems communicate by radio waves using one of the frequencies allotted by various government agencies.
With battery-powered radio frequency wireless intercom units, a person can carry a station as they walk around.
Ideally, the best intercom for an application would be one that is in a frequency not in use in the surrounding area, or one that uses digital spread spectrum to reduce possibility of interference.
[5] The first intercom systems communicated over a set of low-voltage signal wires installed in the walls of a building.
Non-radio "wireless" intercom designs were developed that used a building's existing electrical wiring to carry communication signals.
This method of intercom connection is most useful in offices and homes served by a single electrical service.