We have listening devices for many purposes and for different conditions. GSM interception devices use the GSM mobile network to send the interception to your phone. You call up the interception equipment that is equipped with a SIM card. The appliance answers your calls and turn on the built-in microphone, so you can hear what is going on in the room.
We also have wireless monitoring via radio waves. It acts as a one-way-walkie-talkie. You can also record conversations or meetings with our listening devices. USB key with built-in microphone allows discreet audio recordings. Or the digital voice recorder that can start an audio recording, when recorded sounds. Read more on electronicsmatter.com