The only compact transmitter designed and built for fitness. Versatility - best describes this system - Built onto Aeromic, Cyclemic, or E-mic - to be worn as a headworn, armband, or waistband transmitter. Specially designed O'ring seals, marine grade varnish on the circuit board, sealed push button 'on/off' switch - sets this transmitter in a class by itself for fitness use. An 8 channel frequency agile transmitter and receiver combo give you the flexibility to operate in the toughest wireless areas.