You may want to search other threads-I seem to recall that someone wired a module (piezo) to their gas cap that chirped when locking/unlocking. MINI fobs are supposed to have a rolling code for lock/unlock.

 

SFMCS ...that twould be me ! .....i have step by step to put a chirp for lock, or unlock ...in my 2016 justa 4 door w/o factory alarm....nice to be able to just walk away and not look back and hear the chirp as i fumble for the lock button on my FOB

here's the thread: https://www.northamericanmotoring.co...-actuator.html that was posted last year on this Electrical forum

back to my original post on this thread: ...again, i put a simple voltage drop after market alarm in my 2004 MC and worked fine ...open a door, dome light come on alarm goes off ..... was a snap to install, one wire to the battery, one wire to ground, one wire to the fan that runs after you shut the car sometimes for short time, done! ...but my 2016 has so many more electronics and some which continue even after the car is shut off which might affect a voltage drop sensor and cause a false alarm .....i know some (cheap) simple after market voltage drop alarms do have a sensor that once you hit the 'set alarm' button the unit will not arm itself until a delay........but i am unable to find out how long the unit's delay feature delays things and if it would be long enough a delay to avoid false alarm......has anyone successfully installed a simple after market voltage drop alarm in a 3rd generation ?