I put my Windows 10 desktop to sleep last night and laid down in bed to engage my own “sleep mode”. Five minutes later, with a frantic rush of cooling fans, my PC woke itself back up. I gave the cheerful login screen the middle finger, shut it down, and made a mental note to troubleshoot in the morning.
There’s tons of forum threads and blog posts on Google about spurious wakeups. My old Windows 7 laptop used to wake itself up for the sole purpose of going into hibernation if it had been left in sleep mode for longer than six hours on battery. My Windows 8.1 tablet…still does whatever the heck it’s doing to drain the battery. And my Windows 10 laptop has occasionally woken itself to do updates.
But the cause of my desktop waking up was none of these. Instead, Event Viewer shows me this:
To verify, I put my computer to sleep while pinging it with arping from a Linux box. Interestingly, even in the brief time it was asleep, arping continued to receive responses. A few seconds later, the machine boot up again.
This can probably be fixed from the BIOS/UEFI. However, another quick fix is to open the NIC settings in Device Manager and either uncheck “Allow this device to wake the computer” or, if you still want Wake On LAN capabilities, check “Only allow a magic packet to wake the computer”. Apparently, by default, the computer can be woken by any packet that is directed to the NIC. In a noisy LAN environment, this is unacceptable.
Note that I still haven’t figured out root cause–what sent the traffic in the first place–but that can come later.