I finally found why my PC was waking from sleep for seemingly no reason

For several months, the author experienced a bothersome issue with their PC mysteriously waking from sleep without any apparent reason. They observed their computer turning on intermittently, without any input from them. To investigate further, they discovered that a third-party application was programmed to wake the PC at regular intervals, though this happened infrequently enough to go unnoticed for a while.

Power consumption wasn't a significant concern, as the author used their PC daily, with the intermittent wakes occurring during regular usage hours. However, after two months, the issue became intolerable and prompted the author to examine the cause. Using an elevated Command Prompt, they ran the command "powercfg lastwake," which revealed that Macrium Reflect, a backup program, was the background process responsible for waking the PC.

The author had scheduled monthly backups with Macrium Reflect, but they hadn't connected this program to the sporadic wake-from-sleep events. On other instances, Windows Update was responsible for the wake-ups. The author had maintained Windows Update on their Windows 11 system, which caused infrequent wake-up events. While they identified third-party apps and Windows Update as the culprits in their case, the author noted that other PCs might have different causes.

Wake-on-LAN (WoL) was highlighted as a common reason behind PCs waking from sleep. A WoL app on the author's phone could have inadvertently caused the issue, and a misconfigured network adapter could wake up on any network packet. The router or mesh system might also wake the PC during status checks, client pings, or device discovery.

Minor reasons, such as accidental movement of a wireless keyboard or mouse, electrical interference from appliances on the same circuit, or even pets or children bumping into the desk, could also trigger the PC to wake from sleep.