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systemidletimerreset (coredll)

coredll is for smart devices, not desktop Windows. Therefore, this information only applies to code using the .NET Compact Framework. To see if information for systemidletimerreset in other DLLs exists, click on Find References to the right.

This function resets a system timer that controls whether or not the device will automatically go into a suspended state.

C# Signature:

static extern void SystemIdleTimerReset();

VB Signature:

Declare Sub SystemTimerReset Lib "coredll.dll" Alias "SystemIdleTimerReset" ()

User-Defined Types:


Alternative Managed API:



To keep a device awake indefinitely, you can use SystemParametersInfo() (also in CoreDll) to query the three idle timeouts SPI_GETBATTERYIDLETIMEOUT, SPI_GETEXTERNALIDLETIMEOUT, and SPI_GETWAKEUPIDLETIMEOUT. Ignoring any values that are zero, use the minimum of these three values as your N, set a recurring timer to fire more often than every N seconds, and call SystemIdleTimerReset() every time it fires. When you're done with your critical operation, kill the timer, and the device will be able to sleep again. I tried this from C# and each idle-timeout value was 0, so I just called SystemIdleTimerReset() every 30 seconds during the critical operation.

You can also look at the configured timeouts at the registry key "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power".

Tips & Tricks:

Please add some!

Sample Code:

    /// <summary>
    /// This function resets a system timer that controls whether or not the
    /// device will automatically go into a suspended state.
    /// </summary>
    public static extern void SystemIdleTimerReset();

    private static int nDisableSleepCalls = 0;
    private static System.Threading.Timer preventSleepTimer = null;

    public static void DisableDeviceSleep()
        if (nDisableSleepCalls == 1)
            Debug.Assert(preventSleepTimer == null);
                // start a 30-second periodic timer
            preventSleepTimer = new System.Threading.Timer(new TimerCallback(PokeDeviceToKeepAwake),
                null, 0, 30 * 1000);

    public static void EnableDeviceSleep()
        if (nDisableSleepCalls == 0)
            Debug.Assert(preventSleepTimer != null);
            if (preventSleepTimer != null)
                preventSleepTimer = null;

    private static void PokeDeviceToKeepAwake(object extra)
        catch (Exception e)
            // TODO


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