struct LASTINPUTINFO
        {
            public int cbSize;
            public int dwTime;
        }
        [DllImport("user32.dll")]
        static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);

        static int GetLastInputTime()
        {
            int idleTime = 0;
            LASTINPUTINFO lastInputInfo = new LASTINPUTINFO();
            lastInputInfo.cbSize = Marshal.SizeOf(lastInputInfo);
            lastInputInfo.dwTime = 0;

            int envTicks = Environment.TickCount;

            if (GetLastInputInfo(ref lastInputInfo))
            {
                int lastInputTick = lastInputInfo.dwTime;

                idleTime = envTicks - lastInputTick;
            }
            
            return ((idleTime > 0) ? (idleTime / 1000) : idleTime);
        }