The circuit board is designed to play 3 different tones. Ding Dong, Ding, or the Westminster Chimes. The circuit is self-contained and runs on a small 2032 button battery. The unit can be hidden anywhere but will need to be hardwired to the doorbell buttons and the speaker. The package comes with one doorbell button but additional buttons can be purchased. You can play a different tone on up to three doors. Front door can play the "Westminster Chimes"; the side door—"ding" and the back door– "ding, dong". The PCB board is only 1.8" square and can be mounted anywhere. The speaker is 3/4" square and looks good mounted on the hall wall inside the front door. The doorbell button is a very small momentary push button—1/8" x 11/64th". The 2032 battery is easy to replace but should last for one to two years with moderate use.