You need to check the range offered – and allow for the manufacturer exaggerating a little! You also have to take into account walls, which interfere with signal strength. Volume is also a factor. You don't want it uncomfortably loud in the house, just so you can hear it in the yard. A wireless doorbell that offers two receivers – so you can put one out the back – is one way around this. The other option is to buy a wireless doorbell that calls your smartphone – then you'll know there's someone at the door wherever you are.