Road Trail Run: Polar OH1 Optical Heart Rate Sensor Review: a comfortable, accurate, and much-welcome alternative to the standard chest strap
Polar Flow Connects With Nike+ Run Club | Polar Blog
Amazon.com : Polar Verity Sense - Optical Heart Rate Monitor Armband for Sport - ANT+ and Dual Bluetooth HRM - Waterproof HR Sensor with only One Button - Compatible with Peloton, Zwift