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.)
- Click Control Panel/Hardware and Sound/Power Options.
- Select the active Power Plan and click Change plan settings.
- Click Change advanced power settings.
- Click Change settings that are currently unavailable.
- Scroll down to the Sleep item and click its plus sign to expand the listing.
- Expand the Allow wake timers subheading.
- Under both the On battery and Plugged in settings, select the wake timers you wish the PC to respond to.
Disable tells the PC to stay asleep — i.e., to ignore the wake timers. Important wake timers only allows some high-priority items, such as some in Scheduled Tasks, to run. Enable allows all wake timers to wake the PC. (See Figure 1: Shown, a typical notebook’s settings; desktop PCs might have different options.)
Figure 1. The Power Options menu lets you control how each Power Plan reacts to wake timers.
- When you’ve made your choices, exit the Power Options menu by clicking OK and/or Save Changes, as you go.
- If your PC has more than one Power Plan (e.g., Balanced, High Performance, Power Saver, etc.), repeat these same steps for each Plan.
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.
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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