I am working on a C# application which runs in the background without any Windows control.
I want to notify Windows that my application is still alive to prevent Windows from going into the idle state.
Are there any APIs available to call from my application which notify the Windows OS that my application is still alive?
You've to use SetThreadExecutionState function. Something like this:
public partial class MyWinForm: Window { private uint fPreviousExecutionState; public Window1() { InitializeComponent(); // Set new state to prevent system sleep fPreviousExecutionState = NativeMethods.SetThreadExecutionState( NativeMethods.ES_CONTINUOUS | NativeMethods.ES_SYSTEM_REQUIRED); if (fPreviousExecutionState == 0) { Console.WriteLine("SetThreadExecutionState failed. Do something here..."); Close(); } } protected override void OnClosed(System.EventArgs e) { base.OnClosed(e); // Restore previous state if (NativeMethods.SetThreadExecutionState(fPreviousExecutionState) == 0) { // No way to recover; already exiting } } } internal static class NativeMethods { // Import SetThreadExecutionState Win32 API and necessary flags [DllImport("kernel32.dll")] public static extern uint SetThreadExecutionState(uint esFlags); public const uint ES_CONTINUOUS = 0x80000000; public const uint ES_SYSTEM_REQUIRED = 0x00000001; } 
0 means the method failed. From the documentation of SetThreadExecutionState - "If the function succeeds, the return value is the previous thread execution state. If the function fails, the return value is NULL." (Note - I am assuming you probably already had figured that out, but wanted to post an answer for completeness and to help anyone else who might come along and view your comment)
You have a couple of options:
Use SetThreadExecutionState, which:
Enables an application to inform the system that it is in use, thereby preventing the system from entering sleep or turning off the display while the application is running.
Where you could use the ES_SYSTEM_REQUIRED flag to
Forces the system to be in the working state by resetting the system idle timer.
Use SendInput to fake keystroke, mouse motion/clicks
SetThreadExecutionState example
// Television recording is beginning. Enable away mode and prevent // the sleep idle time-out. SetThreadExecutionState( ES_CONTINUOUS | ES_SYSTEM_REQUIRED | ES_AWAYMODE_REQUIRED); // Wait until recording is complete... // Clear EXECUTION_STATE flags to disable away mode and allow the system // to idle to sleep normally. SetThreadExecutionState(ES_CONTINUOUS); You can use SetThreadExecutionState described here:
Since it is a Win32 API function, to use it from C# you'll need to PInvoke it. The steps are described here, including a sample method PreventSleep to temporarily disable sleep mode:
i know this is old, mine is a console program
class Program { [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)] static extern uint SetThreadExecutionState(EXECUTION_STATE esFlags); public const uint ES_CONTINUOUS = 0x80000000; public const uint ES_SYSTEM_REQUIRED = 0x00000001; ####then call this below code public static void keepalive() { int x = 0; for(; ; ) { x++; SetThreadExecutionState(EXECUTION_STATE.ES_DISPLAY_REQUIRED | EXECUTION_STATE.ES_SYSTEM_REQUIRED | EXECUTION_STATE.ES_CONTINUOUS); Console.WriteLine("Preventing lock screen.... disabling proxy"); setProxy("", false); Thread.Sleep(10000); if (x == 10) { x = 0; Console.Clear(); } } } 
I don't think there's any way to do this directly in managed code.
A quick search reveals this post from 2 years ago. Basically you'd need to do some interop to call a raw windows API.
