my alarm used to trigger when the car got hot from the sun at the hottest part of the day which in australia is all day, to test if it was the bonnet sensor i disconnected it, has not happened since. the likelyhood of people wanting to get under my bonnet is zero. but it dont have a 2010 plate so i havnt bothered to replaced it, but im sure a repalcement sensor would fix my problem. if i learnt anything from my short ownership i reckon RR probably use the same sensor from 2003-2012

Adam, a little known fact for you... If you open your bonnet then pull the bonnet switch UP “you will hear a small click” and it thinks its closed!

You can remove said bonnet switch plug it back in pull the top up and test it for a few days...

I had the same happening to me in my previous L322. Very common fault. I put a piece of self adhesive plastic under the bonnet right above the switch and that sorted it. I had previously put a new switch in but that didn't solve it. This piece of plastic did. Try it.

Just found a bonnet switch for L322 in one of my draws if anyone's interested I'll happily post it if you PM me your address.
They are branded BMW funnily enough!
Changing the switch didn't solve the problem with mine though. You need to put something between switch and bonnet to keep the button pressed otherwise the car thinks your bonnet is open. I did that and haven't had any "Bonnet Open" messages or false alarms since.

it does seem like the BMW bits on these are the least reliable parts!