Laptop turns on spontaneously

In the space of a week I noticed three different laptops and a desktop (all different brands, and all with XP) that appeared to be off and then without me doing anything they turned on!  I thought there must be some new Microsoft update that must be causing this odd behavior.  After a bit of research, I realized they were only doing what they were told.  In the “Power Options” in “Control Panel” they were all set to “StandBy” after 20 minutes and “Hibernate” after 45 minutes.  I had just happened to come across all four of these machines when they were waking up from StandBy to move into hibernate mode.