Modern bedwetting alarms are generally designed with a sensor probe and a very loud buzzer. The probe goes in the pants and the buzzer goes by the ear. At the first drop of wetness, the buzzer goes off, wakes the child, who gets up and goes to the bathroom. Over time, the child's brain begins to associate the urge to void at night with that obnoxious buzzer, and starts to awaken before it goes off. At that point, he's dry.
Relapses are common but usually easy to retrain quickly with a week or two back on the buzzer.
I tell those parents to wait six months or so and try it again when the child hopefully doesn't sleep quite so soundly. If you wish to use an alarm, it is helpful to have some good instructions for managing the nighttime alarms. It is also well to keep in the back of your mind that bedwetting is sometimes a symptom of obstructive sleep apnea , a potentially serious condition. A sudden onset of significant bedwetting in a previously dry school age child could also mean diabetes or urinary tract infection as well. Notify your doctor if your child's bedwetting seems out of the ordinary.