Smart locks are awesome, I have a z-wave lock in my house, hooked up to a home automation system I wrote so that my front door unlocks whenever I walk up to it. I love that I've reduced the "wallet/phone/keys" patdown to "wallet/phone".

Unfortunately, many of the smart locks that use your phone as an unlock mechanism don't have a good solution for what to do when your phone battery runs out. Usually the answer is "use a key", but the new problem is that once enough of your locks are smart, you stop carrying keys.

In the home, keypads work well (and they can easily be set up for guests, etc), but that seems prone to memory error in hotel situations.