Apple Watch and iPhone supports connecting a Bluetooth-enabled strap or monitor.

⌚ Connecting an external heart rate monitor to your Apple Watch

1. Make sure your heart rate monitor is discoverable.
2. Launch the Settings app on your Apple Watch.
3. Tap on Bluetooth.
4. Tap on the name of your device under Health Devices when it appears in order to pair it.

📱 Connecting an external heart rate monitor to your iPhone

1. Put on your HR monitor.
2. Go to the Settings app.
3. Tap Bluetooth and select your monitor.
4. Tap the "More" tab in the N2R app
5. Tap on "Settings"
6. Scroll down and enable Bluetooth heart rate monitors (switch will turn green)