I have been asked this by a few friends after I started this in 2017 and the reason actually is pretty simple. Most locks, especially electronic ones, are wildly insecure but at the physical but also the electronic level. After watching a few Defcon talks as well as lockpickinglawyer on Youtube you can watch them open locks in mere moments. Many electronic locks use some magnet that one can easily override, or has wires exposed to allow you to override, or just uses a poor lock physically. If I was going to put an IoT lock on my house I wanted to be sure of its quality.
That being said, I of coarse started with a poor quality lock to start with. I originally was looking at the Morning Industry RF-01SN which I choose because it had most of the components I didn't want to touch or work with already. It had the lock and tumbler for a deadbolt which I could replace with a better one latter, it had a battery compartment, it had a motor, and fit most doors already. One thing is certain and that like all other IoT products, its over priced for what you get. First order of business however was cutting out all of the electronics within it.
So my first mission was to design a board that could do the IoT function as well as the lock function. For that I have picked the ESP32 to handle IoT as it can do bluetooth, Wifi, and has enough pins to communicate with the RFID chip as well as drive the H-Bridge for the lock motor. For the RFID I have chosen the PN7150 which handles 13.56MHZ RFID, for the tokens to pair with it I have went with DesFire tokens which I found a helpful tutorial for here.
Sadly this is about where I stopped. I don't have the equipment currently to design an RFID antenna to stick in the lock side of the deadbolt. I tried a few pre-built ones and none quite fit so I plan on designing a flex pcb so that I can get the coil close enough to the reduced range DesFire Tokens.