Using Ikea smart lock (Rothult) as a battery powered RFID reader

So I was roaming Ikea last night to find there air quality sensor, but it was sold out.

I happened to find a smart lock called Rothult instead.

It seems to have very good battery life, 17 months with 3 open/close per day according to IKEA.

I was thinking to hook it up to a Aqua smart button or something similar so when the correct RFID chip is read it will send a event to HA that will disarm.

But my first issue was that the lock. It will actually lock using any card/chip that I have, but then only unlock using the masterkey card or last chip/card used to lock it.

I found a github repo where a guy flashed a new firmware so he could communicate with it via serial.

So a new firmware would be ideal, but just not sure how to get on with that.

Anybody that has some good ideas?