Make sure that Bluetooth is turned on in your phone’s system settings. Follow these steps:

1. Power cycle your Doppler.

2. Forget/unpair the Doppler from your phone’s Bluetooth paired devices list.
3. Press the Bluetooth button  on the Doppler so the Bluetooth button is blue.

4.  Connect your Doppler to your phone’s Bluetooth settings. 

5. Try a different device.