You don't. There is no such thing as night time potty training. It comes as their bladder grows and their body is able to produce the proper chemicals to either wake them up or clench the muscles all night to hold it. It is beyond your child's ability to do this. He may not be able to do this until he hits puberty. Most are able by 6-8 years of age.
The wet does not wake them up. The trying to wake them up to go does not work. They are trying to learn to hold it mentally and waking them up only disrupts that process. Alarms only make more laundry, they wet, the alarms goes off and wakes EVERYONE up, then the bedding gets changed, clothes changed, shower and new PJ's, and then they fall back asleep and the alarm goes off in a few minutes because as soon as they fall asleep the muscles relax and urine comes out...it's a vicious cycle and it does not work.
Keeping him in pull ups is a convenience for you. I have no interest in washing pee filled sheets, blankets, pillows, bedspreads or comforters every single day. It makes my utilities (elec, gas, and water) go up, laundry soap, bleach, dryer sheets, etc... all cost more since I am using more. Plus my time.
I have worth, I am a person with wants and needs too. I should not have to stay at home and wash the same laundry every day. I work 3 part time jobs so when I have the option of doing something enjoyable I take it.
I love doing laundry, it's my favorite chore. But I am not going to increase my laundry by not buying pull ups. They are about $0.50 each, less than a dollar a day.