Polar Stride Sensor Bluetooth® Smart 91053151 *The item for sale is only what is shown in the first photo. There are no instructions or box. *Please understand that this is a used item before purchasing. The following is from the manufacturer's website: The Polar Stride Sensor Bluetooth® Smart is perfect for improving your running technique and efficiency. It uses a highly sensitive inertial sensor to quickly and accurately measure speed, distance, cadence, and stride length. Compatible with Bluetooth® Smart Ready devices that support running speed and cadence service functions. You can use the sensor with many common fitness apps and Bluetooth® Smart-equipped Polar products. Please check support.polar.com for compatible products.