Windows – How to find out which application is causing the computer to sleep

hibernatesleepwindows 7

My computer went to sleep (actually, it looked more like hibernating) in the middle of an active time, without any warning.

In the Event log, the message was:

The system is entering sleep.

Sleep Reason: Application API

It doesn't give any other information. Is there a way to find out which application caused this call?

Super useful for more than this situation, but a lifeline when trying to troubleshoot sleep / shutdown / hibernate issues.

Workaround

Your system might not be fully compatible with Windows 8/8.1. If you don't need hibernation, you can turn it off entirely:

Open a command prompt as administrator.
Type or paste the following command, and press Enter to run it:
```
powercfg -h off
```
Changes are applied immediately.

You will regain some disk space which was previously reserver for the hibernation file (hiberfil.sys). By default, that's 75% of the installed RAM.
The fast startup feature will be disabled, too:

Starting with Windows 8, a fast startup mode is available to start a computer in less time than is typically required for a traditional, cold startup. A fast startup is a hybrid combination of a cold startup and a wake-from-hibernation startup.

_{Source: Distinguishing Fast Startup from Wake-from-Hibernation}