ETA: for those who used the alarm and it worked, great. I'm happy for you. For those who slept in wed beds and sleeping bags, I feel your pain. But please don't say that others are "talking out of our asses" when we DID use the alarm, as directed, for months, to no avail. My kid wasn't dry until he was 12 - without medication that is. And he was exhausted from being wet or awakened by alarms at night. So I know what it's like. It had nothing to do with his motivation, or ours. It had to do with his biology. We found success with another path - explained below. So everyone should consider their own situation and choices.
Original post: We used it - and it was absolutely pointless. It only goes after AFTER the kid is wet, so what's the benefit? Yes, it wakes everyone up so you can run in and start stripping off pajamas and changing sheets, but it's closing the barn door after the horse has escaped. What exactly is it "training" him to do? He was asleep when he peed, so there's nothing to train him in, no "advance warning" to cue him in to. Do you see where I'm at with this?
My kid was late to figure out using the potty during the day, and even later at night. We had good conversations with the pediatrician and a pediatric urologist to whom she referred us. Believe me, I understand how much you want this problem to stop, but there's more to it.
There is something called nocturnal enuresis - which is nighttime bedwetting. Now, depending on what you think the right (or average) age is for waking up when the bladder is full, a child may not have N.E. but may not "be there yet" developmentally. So whether a 5 or 6 year old is just "not there yet", or whether N.E. is present and likely to be so for years to come, you can't know right now. According to the urologist, N.E. is present in a lot of kids, more often boys but there are plenty of girls, and that can go on up until the age of 18 or so.
Looking back on all we went through, I would skip the alarm entirely. I don't know anyone for whom it has worked. I don't think nighttime dryness is "trainable" - I think it's developmental because the full bladder has to signal the brain to wake up before the sphincter muscle lets go.
By the age of 7, we weren't seeing any changes at all. We opted, after discussion with the urologist, for a nighttime dose of a medication called DDAVP. He indicated he had middle and high school kids on it. I'm not thrilled with medication and I avoid it as much as possible. But our kid wasn't going to sleepovers, and he wasn't getting a full night's sleep. After 7 years of never going all night dry, we chose meds. I wouldn't do it at 5 if a child could sleep through the night with a pull up or a Good Night product, but by 7 or 8, yes, it's worth it.
So, wait it out, or do anything else. But the alarm is nothing but frustrating, expensive, and useless.