I used to have a wireless doorbell. The button and the sounder were'nt physically connected. If it stopped working, you had to try to work out whether the battery had run out in the button or the sounder. Recently, it stopped working. I tried to change the battery in the button. It was an unusually small type of battery, and fiddly to change. Afterwards, I found it impossible to put the faceplate back on the button - eventually, one of the little plastic lugs that was supposed to hold it together snapped. So I got this instead.
Why have something that needs batteries and can go wrong, when you can have something that doesn't need batteries and can't go wrong?