My computer used to wake itself up at 3 AM like it had somewhere to be. The screen would light up the bedroom, the fans would spin up, and I would stumble over to check if someone was hacking me. It was just Windows being Windows. Something in the background was poking the machine awake, and it took me a while to find out what.

Find Out What Is Waking It

Before you can stop it, you need to know what is doing it:

1. Open a command prompt as admin and run: powercfg /lastwake. It tells you the last thing that woke the computer.
2. Run powercfg /devicequery wake_armed to list every device allowed to wake it.
3. Look for the usual suspects: network adapters, mice, keyboards, scheduled tasks.

The Fixes That Work

• Disable wake timers. In Power Options, go to Sleep settings and set Allow wake timers to Disabled. This stops scheduled tasks from waking the machine.
• Open Device Manager, find your network adapter, go to Power Management, and uncheck Allow this device to wake the computer. Network traffic is a top wake trigger.
• If your mouse wakes it when you bump the desk, uncheck the same box on the mouse. Do the same for the keyboard.
• Type powercfg /devicequery wake_armed again to confirm the list is empty.

What I Learned the Hard Way

• Windows Update loves to wake machines. Set active hours in Windows Update so updates run during the day, not at 3 AM.
• Some routers broadcast magic packets that wake computers on the network. If you disabled everything and it still wakes, check your router’s wake-on-LAN settings.
• Do not just disable wake timers and call it done. The network adapter setting is the one that gets most people.

The Result

Once I disabled the network adapter wake and the wake timers, my computer slept through the night like a log. Powercfg is your friend here, it shows you exactly what you are fighting. Ten minutes of digging, and the 3 AM light show was over.