I see you're downvoted, but I know Yale's residential electronic door locks [1] have a 9V battery terminal on the outside, such that you can open the door in ca

I see you're downvoted, but I know Yale's residential electronic door locks [1] have a 9V battery terminal on the outside, such that you can open the door in case of an extended power outage. (For short outages the lock has a small internal battery.) [1] http://www.yale.co.uk/en/yale/couk/productsdb/smart-locks/Keyfree-Connected-Smart-Lock/ http://www.yale.co.uk/en/yale/couk/productsdb/smart-locks/Ke...