Hi I don't have an aswer for you but I have been bought the same one for Xmas and I have exactly the same problem. I have tried the sensor right next to main system, a few feet away, outside etc. but still wont register the sensor. I have tried changing batteries in the sensor (both sets brand new). The sensor is flashing red light periodically but not sure what this means. Should the sensor light be on all the time?
If you find the answer, please let me know and I will do the same if I find the answer.
Kind regards
E Riding