View accurate heart rate information on all Polar training products (uses both 5k Hz & 2.4 G Hz W.I.N.D. transmission for maximum compatibility) Put it in your gym bag. 5k Hz coded transmission also means that you can see real-time heart rate on compatible gym equipment. Look for the Polar logo! Transfers heart rate information while swimming with products which support 5k Hz transmission* New enhanced user-replaceable battery mechanism Compatible with: FT1, FT2, FT4, FT7, FT40, FT60, FT80, RS100, RS300X, RS400, RCX5, CS100, CS200, CS300