Hellllp, this has happened twice recently, during/after heavy rain, the alarm goes off the rear brake lights come on and the keyfob becomes un useable, none of the buttons on the fob do anything and I can only access the car by using the key in the drivers door, once in the car the key will not turn in the ignition, like it doesn’t recognise the key at all, the first time it happened a while back it kind of reset itself and everything worked fine until it did it again last night/this morning.....started happening at about 12.30 last night and is still happening now 🥴🥴🥴

Ok so update on this weird fault....
Yesterday morning I disconnected the battery and left it until about mid day, reconnected the battery and everything appeared normal, the wife went out for an hour in it to do the shopping,(I did suggest she took her own car....just in case....but no, wanted to go in the fatty) all was fine to start with, a trip across town about 4 miles, no problem, the return journey back to our village, seemed ok, the daughter stayed in the car whilst ‘er in doors popped into a local shop, when she came out the daughter popped the boot using the buttons on the key, all fine, wifey went to start the car and nothing, key wouldn’t work again...none of the buttons nor in the ignition.. and the rear brake lights had come on again?? No alarm this time as it wasn’t set I suppose?
Called the AA to get it recovered, was told over two hour wait, so thought I’d disconnect the battery again to see if that worked..nope, tried again but left it for longer....nope..but strangely all the windows tv/radio and central locking did as long as the key was in the ignition even though it wouldn’t turn nor seem to be recognized...then I started to get a nasty nuff of what I think was burning plastic/wires coming from the center console area, quickly disconnected battery again and went off for a coffee at home while waiting for the recovery truck. Went back to the car at said time to meet recovery guy, checked with them when I got there to see how far away they were to be told they were very busy and it would probably be at least another 2 hrs.....thought I’d try reconnecting the battery...no burning smell but still no start etc so off home I went for another brew....recovery guy rang hour and half later to say he was with the car....reconnected the battery so we could unlock the passenger side door to suss out how to get the car into neutral we thought we’d just try the key in the ignition....and yep you’ve guessed it...bloody thing worked...he followed me back home to make sure I got back and then went...not five minutes later I looked out of the window and the brake lights were on again and yep the key wouldn’t work again, have manually locked it and disconnected the battery....just need to get time now to see if I can work out what the heck the problem is?? Obviously an electrical fault but where to start
Sorry for the long ramblings

I may be off kilter but this is usually related to the BCM under the passenger seat I think, mine used to do exactly this when parked down hill in rain someone with a bit more knowledge will hopefully be along soon

Ahhh ok thanks buddy, gives me a start point, did yours smell of burning/melted plastic or wires? Could explain the niff near Centre console, Is it easy to get to or is it a seat out job do you know?

Removed both the BCM and the LCM sat them on a radiator in the house for a couple of days as someone had suggested they may get damp, refitted them and reconnected the battery and hey presto all seems fine....didn’t even bong up with HDC inactive etc faults.
will keep my fingers crossed but only time and more puddles will tell 🤣🤣

So update again....was fine for a couple of days, then a bit more rain and puddles and it’s started playing up again back to the drawing board and trawling the tinternet

Have you tried switching the internal alarm sensors off when you lock the car?

I don’t think it’s anything to do with the alarm, it sees to be a water ingress problem, somehow getting into either the lcm or the bcm? I think it may (hopefully) be blocked sunroof drain tubes?