Currently, Windows Phone only supports the RFCOMM protocol via Bluetooth 2.0. The device’s minimum hardware specification does not currently include BT4.0 LE - although some of the devices support it, it does not work in the API. This is because health devices using BTLE support the GATT protocol and the current proximity stack using RFCOMM, which allows you to create scripts, such as support for a serial port profile.
This gives us devices such as Sphero and MetaWatch that can connect to the phone - but, unfortunately, not the latest generation of devices for health and fitness.
Polar is currently making a BT 2.0 heart rate monitor if you want to connect something with your 920 :)
Lewisbenge
source share