Alternative tones for front and back doors Two to one ,front & back door function .With flashlight and dual-tone selectable system , you can freely decide different tones for front and back doors.So it is easy to confirm the location of guests. **************************************************************** Remote Range: 80-150m Sound: two kinds of lovely sounds for selection Power supply: DC4.5v Shell material: ABS plastic Certificate:FCC, CE, CCC, Package:Blister