My WiFi-connected IOT devices run on a separate network, with outgoing connections disabled, but that's more out of a privacy concern.

I'm a big fan of IOT and home automation, with one exception: door locks. I wouldn't trust any electronic device with my door lock. There's just so much more that can go wrong, both from a technical and a security standpoint. Also, electronic door locks aren't THAT more convenient than my physical house key.

With locks it's kinda reverse that a homebrew solution might actually be more secure than a commercial one (consumer grade at least). Mostly due to security by obscurity. The average thief won't take the time to reverse engineer your lock solution but just pick the next best break-in option which would be smashing a window or breaking the lock/frame. (Unless of course you have really dedicated enemies that want to specifically get something, but then no solution would be perfect. They will just bash your door in with an axe). But a thief might scan for Bluetooth signatures of known broken lock systems and just do drive by brake ins that way.

I'm thinking of building a elektronic lock solution myself because it would actually increase security for me. As currently I often neglect to lock the doors when going to the back of the yard. Mostly because I don't have the key on me. And my kids are at an age that they will still neglect it for many years. A quick drive-by thief could be in and out in no time. An electric lock with a rfid and keypad would be a proper solution as it always locks when you close the door and are never locked out (unless the power fails but then you use a backup key stored somewhere safe).

An electronic lock doesn't have to be impenetrable, just take more than 5 minutes to break into. This is about as long as a determined thief might spend picking/breaking your regular lock before they're in or they move on to the next target. If you add a bit of obscurity in the mix you could be just as safe. A smartlock that looks like a regular lock, or has all the "smart components" on the inside of the door (like smart bolt-on key turners) would not stand out.

I have a story for you. You see my daughter had hard time turning the key in the old lock. Somebody else had to open the door for her all the time when she was coming home from nearby playground. Even she had her own key she was lacking physical power to turn the key.

So my solution was to buy an electromagnetic lock, which also could be opened by key in case of power outage. And I did exactly this - an RPi was in charge of opening the door via my private WiFi network so when my daughter was coming home, she was connecting her smartphone to my WiFi, launch an app I also wrote and used that to open the door.

Now the funny thing is that the electromagnetic lock was so sensitive that it required a lot less power to open it via its mechanical key so she ended using that most of the time, only in rare occasions of a new friend she was showing off that she is able to open the door via phone.