Are you saying that this is a house rule in your listing? If it’s directly stated in your listing ( that car alarms cant be used late at night, then you have a leg to stand on. So even if he did stay at another guest of the wedding, and also happened to feel uncomfortable, at least you can state that this was a house rule, already established. If not, then perhaps it should be. If youve made the same request of 400 guests, then its obviously a consistent issue.