Transmitters that use the electrical wiring in home or office and using carrier current technology. You can spot intercoms and monitors when the sending unit plug into the wall electrical socket. When the sending unit does not plug in, it is not a carrier current system.
Carrier current wireless audio intercoms are transmitter and receiver sets use home AC wiring. They get the power for the units from the outlet. They use the same electrical wiring as a antenna to transmit {on various radio frequencies} and receive the signals from one unit to another. This is why sometimes they don't talk to each other if they are plugged into different circuits. They don't pass though some plug strips and
The signals going out on electrical circuits {carrier current signals can be carried over great distances} can be picked up by anyone nearby who has a wireless idevice operating on the same frequency or anyone with a frequency scanner looking for that type of emission.
You might consider child or room monitors amount to self-installed bugs.
Intercoms and sensors that are battery operated or use transformer power adapters use radio signals sent through the air and not your electrical wiring.
