Polar H1 Heart Rate Sensor Kit
The Polar H1 Heart Rate Transmitter Sensor Kit features the latest Polar soft strap design for maximum comfort. The H1 heart rate sensor kit is the replacement for the Wearlink+ transmitter and features coded 5kHz transmission. The H1 can also be used as an upgrade for the venerable T31 or T31C transmitters.
Please see this link for its replacement.