WearLink+ transmitter with Bluetooth wireless technology improves the training experience of Android RunKeeper app users by adding heart rate monitoring. This enables you to train with heart rate and get more out of RunKeeper activities. WearLink+ transmitter with Bluetooth provides heart rate data to the Android RunKeeper app, helping you to understand how hard your heart is working in any given workout. The Bluetooth transmission ensures that the mobile device using a mobile training application picks up the right heart rate signal and not someone else's. Note: This product is not compatible with iPhone.