Small size,easy to paste on the wall,once people coming,it will detect Features:It is light-control sensor doorbell which operated by 3pcs of AAA size batteries(1.5V).Install the doorbell on the access,and turn it on.When clients come,it will automatically detect and said” Hello,welcome”or other tones. The detecting distance is from 3 to 7ms. Widely used for shop,supermarket,stores…..We advice to ...