Noticed it today.
Normally if the door is left open or ajar and you try and lock it with the fob it will give a double beep of the horn to let you know, didn't happen.
Had the passenger side door open accidently pressed the lock on the key fob. The doors locked and no double beep came from the horn.
I tested the other doors and same thing, door ajar or open, made no difference.
The door open/ajar light in the dash still lights up though.

Any theories on a cause?

And to add to this, when I unlock it, open the door then close it or leave it open, it will relock it self after 30 sec

Check the switch by changing it with a back door switch

check the door switches. They are the little black 'knobs' on the bottom of the door jam that point out towards the doors. Undo the screw and see if it does the same thing. The screw grounds it against the car. It might be loose/ a switch on the way out. happened to my car it stopped telling me my lights were on and i got 2 replacements from teh wreckers and bamn all fixed

Happens regardless which door is opened, so, might have to change all 4

Nah, something else is afoot.

I will text you.

Mike

If it was the switches the light in the dash would not light up.

My interior lights light up as normal on unlock and fade out on lock and the security light lights up and goes out as per normal.