This is the Scubapro HRM Belt Heart Rate Monitor Belt

Features:

• More comfortable to wear with soft elastic chest strap
• More reliable ECG transmitter provides a patented skin temperature measurement that's factored into your decompression algorithm, helping to make diving safer and more enjoyable
• Convenient heart rate monitor can be clipped on/off from the elastic belt so the belt can be rinsed and dried fully post-diving
• Compact design saves space in your dive bag
• Belt can be used for diving, swimming or exercising
• Compatible with SCUBAPRO HUD, Galileo 2 and A2 dive computers
• Heart Rate Belt has an operation depth of 120 meters / 394 feet
• Powered by a user replaceable CR2032 type battery, that lasts for around 50 dive hours or 1 year.

Factoring your heart rate into your decompression calculations helps make diving safer and a lot more fun. A lightweight waterproof ECG (electrocardiogram) transmitter is clipped onto the elastic belt that straps around the chest, directly against the skin. This belt wirelessly transmits your heart rate data to your SCUBAPRO personal dive computer. Data is displayed on the screen, plus is factored into your decompression calculations to create a more personalized dive plan and improve the quality of your diving.