What's waking my desktop?
 

Windows 8. I have to explicitly shut it down over night, as in hibernation it starts up again in the middle of the night, around 4 am. It's likely something wanting to update or do some maintenance, but the event logs don't reveal much, only that it started up, and when. I've tried turning off Avira automatic update, no joy.

What else can I do to find out what's going on? Or order it to stay in hibernation until I allow it to wake up?

It could be a switching pulse that is sent down the mains line to control lighting and other such stuff.

I had a puter the used to do the same thing about the same time (in Oz)

As a temporary fix just remove the power lead from the wall socket. If it still turns on over night, consult an exorcist.

The cat is awake at that time of night

My Dell has been doing that periodically for years.

Screen set to go off after five minutes inactivity but even lights up with no internet activity or anyone walking around. Most puzzling.

Using the command line, try these to find out what's causing it:

powercfg -lastwake

That should tell you the source of the wake command.

powercfg -devicequery wake_armed

That one should tell you which devices are set to wake the system, similar to looking at the power options for every device in device manager.

powercfg -waketimers

That one will tell you which, if any, programs have wake timers configured.

Powercfg is a really useful cmd line tool in these situations. :-)

Vulcan.... If you have a laptop running W7 there is a setting, too late in the day now to expand. Briefly there is a setting to extend battery life reduced to 80% of charge.

Even after removing power lead from wall socket, the battery kicks in, mainly to drain battery power and recharge when back on mains power.

belfrybat,

https://support.microsoft.com/en-us/kb/2799178

You could try disabling Wake on Lan in the BIOS.

Oy chaps, Mr Bat says it's a desktop!
So turning it off at the wall would certainly do it...

Sorted, Tonka and mixture had it spot on. Can't imagine how anyone thought that was a good idea. Disabled the automatic turn-on and set it to a time when the puter is likely to be on.

Turning it off at the switch is what I wanted to avoid, as the inrush current affects filter capacitor life.