@Teresa1601 I have had guests lock themselves out with a keypad. Some people just automatically turn the door lock on the knob and then the keypad doesn't work. My older guests tend to be the main culprits of this. I have taped the knob lock and leave instructions in multiple places asking guests not to do this. I also hide a key on the property after having to do a few rescues. Some people are super uncomfortable with even basic technology (we sometimes get feedback that guests can't figure out Netflix on the smart tv when its literally a big red button on the remote.)
In this case I would just say "I am so sorry I was not able to unlock your door right away. I have hidden a key for you to use in the event that you would prefer to secure the space with that instead. (Give location.) My mate/cohost/neighbor/friend/child is also standing by if you have difficulty contacting me during the remainder of your stay. Here is the number. Let me know if there is anything else you need."
I ALWAYS leave a note with 2 phone numbers for guests to call during emergencies when they check in. Sometimes I am not able to get to the phone immediately either, so it helps to have a back up.
If it helps I am at least 30 mins from my cottage (more like 45 once I stop what I am doing and get ready to head over) so one hour response is totally reasonable. Guests are expected to be able to get themselves in and out of your accommodation after check in. But it never hurts to have a back up plan or two.