Q. How Can I Sleep Train My PC?

Q.  I have a strange problem with Sleep/Hibernate on my PC. If I enable Sleep/Hibernate, the system wakes up without prompting at times that seem to vary from about 11 minutes to about 50 minutes — in the instances I’ve measured. It happened several times overnight before I realized what was happening.

I have tried eliminating any relevant items in Windows’ Scheduled Tasks.

This didn’t happen under Windows 7, but showed up with Windows 10. However, I’m not actually sure it started with the Win10 upgrade.

It makes no difference whether I select Sleep/Hibernate through the Power Options settings, by command line (i.e., shutdown /h), or with power-off button. I can avoid the problem by closing down fully, but it's more convenient in the mornings to simply wake up my machine and pick up where I left off.

Why won't my computer sleep properly?

A. This is almost surely caused by the PC’s wake timers — software components that can wake an idle or sleeping system to perform functions such as checking for updates, defragging a hard drive, and so on.

Wake timers are built into various parts of the operating system, including, as you surmised, Task Scheduler. But they can also be part of other software; especially software that runs in the background.

Moreover, some hardware devices (or their drivers) can cause a sleeping PC to come awake, entirely separately from any wake-timer activity.

But wake-timer issues are more common, so I’ll start there.

XP and Vista offered scant control over wake timers. But with Windows 7, Microsoft added some wake-timer controls to the Power Plan settings. Here’s how to access and change them on Win10 (Win8/7 are very similar).

(Note that different types of PCs — e.g., portables versus desktops — have slightly different wake-timer options. I’ll discuss a typical notebook’s settings; adjust what follows for your specific situation.)

If your PC still wakes unexpectedly, a hardware device may be responsible. To see what’s going on, open an admin-level command window and enter powercfg -lastwake at the prompt. This will typically show the last device that caused your PC to wake up.

(Alternatively, you can see a list of all devices allowed to wake the PC by entering powercfg -devicequery wake_armed at the prompt.)

Now, open Device Manager, locate the device responsible for the unwanted wake-ups, and right-click it. Open the device’s Power Management tab and deselect (uncheck) the option, Allow this device to wake the computer. Click OK and exit Device Manager.

Figure 2 shows the relevant setting on a network controller; other hardware devices have similar settings.

Realtek power options

Figure 2. Disabling Allow this device to wake the computer can stop unwanted system activity.

With wake timers controlled via Power Options, and with devices’ ability disturb your PC’s slumber disabled via Device Manager, your PC should now be able to sleep through the night.

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Editor's note: We feature an abridged Q&A from Fred Langa's LANGALIST, a column available exclusively to paid subscribers of the Windows Secrets newsletter,. What you see here is just a small sampling of what Langa's writing for the newsletter — go here for more information on how to subscribe.