I'll second that. You also need a range of security codes so that you can eliminate interference to/from your neighbours. Go for the longest range you can find - brick walls attenuate the signal considerably.
Think about the Friedland doorbell extender - allows you to keep your original bell, but also sounds the wireless bell so only one push needed. You can alse power you receiver from a suitable wall wart if it stays in one place for most of the time.
Malcolm