GSM bugs (listening devices) use mobile phone networks to enable the user to dial in to the bug from anywhere in the world in order to listen in to what is going on around the unit.
Bug function:
you dial in to the bug from anywhere in the world and listen in to any audio occuring within a 20 feet radius. The microphone is very powerful and will pick up conversations and background noises.
The Bug is supplied complete with a 3AA battery holder. This will power the unit for about 4 days, but battery life will be shortened depending how often you dial in to use the bug function (please note that very cold weather may also shorten battery life) .