PIECE OF CRAP. DO NOT BUY THIS. IT TOOK A WHILE TO TRAIN MY DOG, BUT HE STARTED USING IT. WE WERE VERY HAPPY. THEN AFTER ABOUT TWO MONTHS WHEN HE WOULD STEP ON IT THE UNIT WOULD RING UNTIL I REMOVED THE BATTERY. PUT IT BACK AND IT HAPPENED AGAIN IN A WEEK. I HAD ANOTHER PAW SO I REPLACED THE BAD ONE. ABOUT SIX WEEKS LATER SAME PROBLEM. I CHECKED THE REVIEWS AND I FOUND SOME OTHER PEOPLE HAD THE PROBLEM.