@Keith0 I host in airbnb and have a team that developed software that delivers reservation specific (unique) codes to guests automatically to a remote lock that doesn't require internet or power (it does require batteries) manufactured by schillage. I had a smart lock but lost internet connection once and it was a mess as I was not ready to hand deliver a key to the guest that day.
We are not commercially available yet but would love to have feedback from other hosts if anyone wants to try it out.
As a disclaimer, I'm a host that happens to have a technology background that developed a solution to a problem I am having with my own rental because I don't believe it has been properly addressed.