There is an app which comes with the lock (you might need to buy a router too) and it is used to oversee the operation of the device. I can enter approximately 30 different codes (each with its own user name such as Ralph - code #1234) and review who has used a code on which date(s) and the various times at which it was used. You're looking at about $150-200 outlay, but it is worth it!
I too was worried about tech failures, but really haven't had any issues. There is a key back-up available should the Internet fail and early warning dying battery alerts. Definitely there is a cost to invest, but it is mimimal. Besides, it appears that you live on-site similar to me, so there is usually someone nearby in case of catastrophic failure (hasn't happened).
Also, no keys for guests to lose. You can change or delete a code at a moment's notice whether you are physically at the rental or not. Most hosts just use some version of the guest's phone number (e.g. last 4 digits), so it is easy to remember.