SUUNTO Heart Rate Transmitter Belt and Medium Strap (T1, X6HR, X6HRM, X6 HRT, X3HR and Advizor) Comes standard with a medium elastic chest strap (24-34.5"); larger or smaller straps are sold separately User Replaceable Battery Compatible with the Suunto T1, and other Heart Rate Monitors: X6HR, X6HRM, X6HRT, and X3HR 100% Water Resistant