Please tap the menu of your WHOOP app and tap “Strap Settings”. From there tap “Pair with a WHOOP Strap”. You will see your Strap listed. To check the serial number of your Strap, unclasp the strap. You will see a white number listed on top of the sensor. Tap the serial number that matches your Strap and tap Connect. Please note the Strap needs to be charged and on wrist in order for it to show as an option to connect.