Hi, Frontier X can pair with any third party sensor that supports BLE connections. Once paired and connected, make sure to double press the red button on the Frontier X to start receiving Heart Rate data on the Garmin. You can check this video to get a better understanding on how to connect with Garmin devices – https://youtu.be/WlE5-flqFu8 . If you need any specific troubleshooting help, do write to us as support@fourthfrontier.com !