The 3rd generation in MIP System technology allows you to choose different sounds for different bell pushes and other transmitters with the flick of a switch so you can identify which door or room has been activated. Single Ding Dong is available on the chime unit but when using selection switch from transmitters 3 other ding dongs can be selected. Requires 2x AA alkaline batteries (not included). The 3rd generation has a huge 175m wireless unobstructed range expandable further by using the MIP Signal Booster accessory. Chime dimensions: H6.0 x W9.0 cm approx.