Accurately measure your heart rate every time with the Timex Flex Tech heart rate sensor chest strap. Compatible with all Timex digital 2.4 GHz heart rate monitors and Bodylink systems using ANT+ technology, the Flex Tech strap fits most body types, with a comfortable fabric that's fully adjustable. The slim sensor also boasts a digital transmission system, helping eliminate crosstalk and interference from other devices nearby. Water-resistant to 30 meters, the Flex Tech strap comes with a user-replaceable CR2032 lithium battery and is compatible with such heart rate watches as the Timex M229, M536, M560, M843, M844, and M878.