The Cadence Sensor 2 fastens to any size crank arm and measures pedal strokes per minute so you can get the most out of your training. ANT+® and BLUETOOTH® Low Energy technology let you send cadence data to Garmin Connect™ and other training apps and compatible fitness equipment for better data when you ride indoors and outdoors. (Water-rated to 1 ATM; ANT+® wireless connectivity does not work underwater.)