The lollipop environmental sensor uses Bluetooth ONLY.
When the sensor blinks blue, it is looking for a connection to the camera using a Bluetooth radio link. The sensor usesBLE 4.1, and it needs to be within 3-4 meters from the camera in its line of sight. Alternatively, under perfect conditions, the sensor can be 10 meters away from the camera. Also, there should be no big metallic objects or appliances (cordless phones, radio toys, other baby monitors that use radio, an independent monitor receiver, etc.) that might generate strong interference with the connection.