Suunto Memory Belt

http://www.heartratewatchcompany.com/suunto-memory-belt-p/suunto-memory-belt-docking.htm
As a recorder, the Memory Belt gives you the freedom to train and record heart rate data in environments where the use of wristop heart rate monitors is challenging or forbidden. Ideal for swimming, team sports, and patient monitoring, the Memory Belt can record more than 24 hours of training sessions without losing a beat.