If an alarm is used nightly your child will likely begin to wake up to the alarm within 4 to 6 weeks. Within 12 weeks, your child will likely be getting up on his own to go to the bathroom or holding his urine until morning.
Once your child stays dry through the night for 3 weeks, you should continue using the alarm for another 2 weeks and then stop. If your child starts to wet the bed again, you can repeat the process. Usually, it takes about 12 weeks of continued trying for this process to work. It is not a quick fix.