In the adapter equipped with a standard USB port there is a built-in GSM audio device. It uses a SIM card that should be inserted. After you dial the number of the card then you will be able to hear anything that's spoken near it. The device has a voice activation function which will make it dial your number.To function away from a power socket there is also a battery that provides two hours independent operation time in listening mode.
GSM listening device in adapter (Nummer: B35)