Article ID: 2800716 - View products that this article applies to.
Consider the following scenarios.
Note If the ACPI Wake Alarm system device is present, it will appear in Device Manager and will have a hardware ID of ACPI000E.
To determine whether the ACPI Wake Alarm system device is present on your computer, start Device Manager, and then examine the devices that are listed under System devices.
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Windows 8 automatically disables the Allow wake timers option for AC power (Plugged in) and Battery power when no ACPI Wake Alarm device is detected on the computer, on all in-box power plans, for mobile computers. Additionally, Windows 8 automatically disables the Action Center / Automatic Maintenance setting Allow scheduled maintenance to wake up my computer at the scheduled time on mobile computers.
All these settings must be changed from their default values for this issue to occur.
The ACPI Wake Alarm device can distinguish the current power source when the device wakes the computer. If this device isn't present, Windows 8 programs the wake event in the Real Time Clock (RTC) before the computer enters sleep or hibernation if either of the Allow wake timers options is enabled under the power plan advanced / sleep option. This behavior helps make sure that a wake event occurs even if the power source changes while the computer is asleep if either of the wake timers was manually enabled.