Casio TM-100 Transmitter Watch
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In 1987, Casio released the TM-100, a most unusual digital watch. On the surface, it appears to be a normal time-telling model but deep inside Casio embedded circuitry to transmit audio signals. Flip the little lever above the display, raise the telescopic antenna and speak or play music into the little microphone and the TM-100 will broadcast the audio to nearby radios! A tiny tuning knob allows you to calibrate the preferred frequency on the FM band (specifically, the Japanese FM band which is 76-90MHz and a portion of the US FM band, 87.5-108MHz). The case is all plastic and it requires two batteries, one for the timekeeping feature and one for the transmitter.