If you want to detect a simple bug the ones that use am or fm waves you could try by detecting feedback with an old radio. Take a radio turn it to the lower end of the am spectrum( the Free part they would use) crank your radio static up and move it around the room. Then try the high end if the am spectrum . Repeat with both sides of the fm spectrum and If you hear a high pitch noise in an area. You might be bugged. PS this is for a REALLY old type of bug that your friend might make.