For me it's only my cat walking over the keyboard or mouse.

The third allowed option (Linux) is wake on lan, which is only triggered through my laptop. I automate WOL events sometimes over cronjobs, when the big machine needs to do some work overnight for some minutes, but very rarely, because it's too loud. But I do those wake up, sleep cycles occasionally automatically when the machine processes big events like the Berlinale, Cannes or Sundance Film Festivals.