It was back about 20 years and called the "OMEGA" Sound Sender. It ran on 2 x AA batteries and the system was mounted on the outside arm cuff of the detector. The receiver was a free Chatelaine am/FM radio. It was challenging setting a FM frequency on the "OMEGA" and trying to get the radio to lock on to the same frequency. It eventually worked....sort off. I often times lost my frequency, having to then try lock on to it again. There was a lag in audio, and the audio sounded tinny. I only used it twice, opting to just continue using the non-wireless headset.