i think there great yet to have a fault with mine, i never had a problem with the collar but rigged to a harness to be on the safe side, mobile phones can alter the reception so turn it off or leave it at home.
hope this helps F.K
take it into the house and warm up an old hat or scarf and put it in with him or try putting them in his bed, one of mine sleeps in an old sock.
all the best, hope he make a recovery F.K