... coming,it will detect Features:It is light-control sensor doorbell which operated by 3pcs of AAA size batteries ... detecting distance is from 3 to 7ms. Widely used for shop,supermarket,stores…..We advice to install it in ... DHL,UPS,TNT,FEDEX.3.We warrantee the goods for one year since customer receive it.4.If goods ... side,we can repair or change a new one for customers if that is not caused by mis-operation ...