Pleasant “ding-dong” sound alerts employees when visitors enter or exit. High/low/off adjustable volume control. Light-reactive sensor has sensing distance up to 15 ft. Wall mountable with angle-adjustable mounting bracket (included). Can be used with door open or closed. Operates on four AA batteries (not included). Gray. 2-3/4w x 2d x 4-1/4h. Shpg. wt. 1 lb.