I actually have electric number pad locks on both doors. They're separate locks; the back door has had one for years and I just installed a new door on the front a couple years ago.

So they technically have two separate keys, but we don't really use the keys. I know the combo to both doors (since it's my home), but my friends living on the first floor only know the combo to their front door.

I like it because they're set to always be locked from the outside, so I never have to worry about whether I locked my door or not. If the door shuts, it's locked. And I don't need to carry a key around. Just enter the combo and it unlocks for 10 seconds.