Retrieving the Operating System Idle Time, Uptime and Last Input Time

We are going into Windows's unmanaged user32.dll library in order to retrieve the operating system uptime, last activity time, and user idle time.

In this C# programming tutorial here at Geekpedia, we’re venturing into unmanaged code again. It’s the popular user32.dll that has the GetLastInputInfo() function which interests us in this tutorial. The application will work with Windows 2000, XP, Server 2003, Server 2008 and Vista.
Start by creating a form with 3 Labels: lblIdleTime, lblSystemUptime and lblLastInput. Also add a Timer tmrIdle. Set the Interval property to 1000 (1 second) and the Enabled property to True. Every time this timer ticks, we’ll check the last input time and the system uptime. Thus setting the timer to tick every 1 second is a pretty good interval for checking this, accurate but not an overkill.

Now let’s write some code. Since we’re using an unmanaged library, first comes the additional using statement:

using System.Runtime.InteropServices;

Next comes the signature function and the definition of the struct that is passed to it:

// Unmanaged function from user32.dll


static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);


// Struct we'll need to pass to the function

internal struct LASTINPUTINFO


    public uint cbSize;

    public uint dwTime;


Now it’s time to double-click the tmrIdle Timer object so that we get to its Tick event. Here comes the main code, which is self-explanatory thanks to the comments:

private void tmrIdle_Tick(object sender, EventArgs e)


    // Get the system uptime

    int systemUptime = Environment.TickCount;

    // The tick at which the last input was recorded

    int LastInputTicks = 0;

    // The number of ticks that passed since last input

    int IdleTicks = 0;


    // Set the struct


    LastInputInfo.cbSize = (uint)Marshal.SizeOf(LastInputInfo);

    LastInputInfo.dwTime = 0;


    // If we have a value from the function

    if (GetLastInputInfo(ref LastInputInfo))


        // Get the number of ticks at the point when the last activity was seen

        LastInputTicks = (int)LastInputInfo.dwTime;

        // Number of idle ticks = system uptime ticks - number of ticks at last input

        IdleTicks = systemUptime - LastInputTicks;



    // Set the labels; divide by 1000 to transform the milliseconds to seconds

    lblSystemUptime.Text = Convert.ToString(systemUptime / 1000) + " seconds";

    lblIdleTime.Text = Convert.ToString(IdleTicks / 1000) + " seconds";

    lblLastInput.Text = "At second " + Convert.ToString(LastInputTicks / 1000);


Retrieving the operating system uptime is done through managed code (Environment.TickCount), however the last activity time is retrieved through the unmanaged GetLastInputInfo() function that we prepared earlier. From then on, calculating the last input ticks is simple math: subtract the last activity milliseconds from the system uptime and there you have it.

Nathan Pakovskie is an esteemed senior developer and educator in the tech community, best known for his contributions to With a passion for coding and a knack for simplifying complex tech concepts, Nathan has authored several popular tutorials on C# programming, ranging from basic operations to advanced coding techniques. His articles, often characterized by clarity and precision, serve as invaluable resources for both novice and experienced programmers. Beyond his technical expertise, Nathan is an advocate for continuous learning and enjoys exploring emerging technologies in AI and software development. When he’s not coding or writing, Nathan engages in mentoring upcoming developers, emphasizing the importance of both technical skills and creative problem-solving in the ever-evolving world of technology. Specialties: C# Programming, Technical Writing, Software Development, AI Technologies, Educational Outreach

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