We don't use keys, after searching and trying out a few different smart locks, we finally found the absolute best one a few months ago and just absolutely love it!
It syncs with your AirBNB calendar so each time a guest books a stay with you, it automatically sends them an email confirmation with their key code. It auto updates itself and auto switches codes for you when guests check in and check out! Saves me a whole world of time and makes hosting not only super easy on me, but easy and convenient for our guests!
Here's a link to it for you to check out:
https://www.amazon.com/AirLocking-Smart-Lock-for-AirBNB/dp/B0759NPC5Y/ref=as_sl_pc_tf_til?tag=airloc...