DESC: Polar Transmitters are an integral part of Polar Heart Rate Monitors. Positioned on the chest, they measure heart rate per minute in real time. Polar Transmitters are ECG accurate and fully water resistant making them the most effective exercise tools for measuring your heart rate. New design for increased comfort Designed for comfort, the new Polar T31 Transmitter is 30% smaller and 25% lighter than earlier models. Built to last The Polar T31 Transmitter is designed to the highest of standards. Polar Transmitters deliver up to 2500 hours of operation or five years of use exercising 10 hours a week. Availability The Polar T31 Transmitter is supplied with all Polar A-series, Polar S120 and Polar S150 Heart Rate Monitors. This product can also be purchased separately. NOTE: The T31 is not compatible with the Protrainer XT, Protrainer XT Cycle, XTrainer, S510, S520, S710, S720i, S725 or S625X monitors. New WearLink is now available. Compatible with all monitors! Polar WearLink Transmitter