The Polar Transmitter is the most advanced unit on the market today. The transmitter is truly the "heart" of the heart rate monitor. The Polar Transmitter utilizes a one-piece design that encases all of the electrical components inside the unit.The Polar Transmitter is the only true 100% waterproof unit available today.No battery compartment or o ring seal to cause leaking and failure.No exposed electronics to cause corrosion.Low power consumption technology means long battery li