No worries, I am up anyway 
We had all the paed checks and they couldn't find a reason for it, as his bladder capacity etc seemed ok, so the alarm weas a last resort and we went through the school nursing team. We got a vibrating one rather than a buzzer and for the first few nights I slept in with him to help him realise that the buzzing meant get up. to begin with, it would wake him as he was starting to wee and would need changing, but with a bed mat on, it meant a change of pjs and a clean bed mat rather than stripping the whole bed. He went through a phase of hating to wear it, but every time he refusedor ripped it off after lights off, he would be soaked to his armpits. Just as we were despairing that he would ever be able to wake himself up, he started waking before the alarm, and then ultimately sleeping through. It's been a bumpy ride though, with good spells and bad spells, him thinking he had cracked it and then having a spell of wet every night for a fortnight.
Like your DS he has a residential coming up and was mithering himself silly about it, thinking he wouldn't be able to go, talking himself into it, tantrums because his mates would be merciless if he had an accident etc etc. He is still worried about it, but tbh whenever he stayed over at friends, even at his wettest, he was always dry in someone else's bed. The nurse said that because they worry about being wet, they don't sleep as soundly as in their own bed.
Have you talked to the school about it? If your DS is going on the residential, it's worth letting them know and then they can help him get the privacy he needs to put a pull up on. My DS though, would rather have not gone than have to face anyone finding out about pull ups, even though he was quite open about it with his closest friends.
It's tough, but he will get there. Monitor the pooing as well, but hopefully that was a one off. Is he ok about that? Did you wake him up to get changed?