Take it from someone who was a wetter herself and is now the mother of one. This is not a potty training issue, this is a physical problem.
The problem with the bed alarms is that they only go off when the kid has already begun to wet, and unless your kids are extremely light sleepers this is not going to wake them up and get them to the bathroom in time. It may eventually train them to wake up and go to the bathroom at the same time every night, but unfortunately it will be about 10 minutes too late. The only benefit to the alarm is in letting you know when your child is most often wetting.
There are a couple of causes for bedwetting:
For some kids it's a small bladder. If that's the case you increase fluids, not decrease them, and have the kid practice holding it a little longer each time during the day to stretch the bladder and improve muscle control. Then you make them go several times leading up to bedtime to make sure the bladder is empty.
For some kids it is a deficiency in the hormone that causes everyone else to produce less urine when they are sleeping. If that is your child's problem then the only thing that will keep them dry is getting up several times a night to pee, which you can train them to do by getting them up on a schedule with an alarm clock. Let the alarm go off for a minute or so and then wake them up by shaking them or yanking the blanket off (however you do it in the morning) while the alarm is still ringing. Walk them to the bathroom and make them go then let them go back to bed. Start this about an hour after they fall asleep and do it every two or three hours, whatever interval it takes to keep them dry through the night. This is the one that worked for me when I finally got tired of wetting the bed at 11 years old, and I still wake up and go to the bathroom about every 3 hours during the night.
The last one is what happens with my daughter. Her bladder doesn't completely relax and release all of her urine when she goes, so as soon as she falls asleep and her body completely relaxes, she wets. This is in bed, in the car, or naptime at school when she was in preschool and kindergarten. For her I have to wake her up about half an hour after she falls asleep (a good bedtime routine that guarantees she'll be asleep at a decent hour is a must). Since she's sleepy and relaxed, she gets the last of it out and we're good for the rest of the night.
If you're worried about sleepovers, there is a medication called DDAVP. It is a synthetic version of the hormone I mentioned earlier that blocks the body from producing urine. Unlike the other medications available for bedwetting, it does not have a cumulative effect and once you've used it a few times and found the dosage that works for your child you can use it only when you need to. So you can do the wake up routine at home and when they want to stay over at someone's house you have the other parent stop liquids early and give them the medication at bedtime. They will not be able to produce new urine for 8-12 hours, and will stay dry. The only potential side effect is water toxicity, which is only likely if you use the medication frequently and do not restrict their fluid intake, since the meds stop them from peeing, and if they keep drinking that liquid builds up in the body. For occasional use this is not a huge concern though. This is what we do with my daughter on the rare occasions that she sleeps over with someone that isn't already aware of the bedtime wakeup routine.