GetIdleTime() in Windows CE/WM does not work?

I am trying to get the device IdleTime by calling GetIdleTime()

[DllImport("coredll.dll")]
static extern int GetIdleTime();

but idle time keeps incrementing even when the device is not idle.

I call the function with a button click and everytime I click the button the time has incremented even when I do it repeatedly. Why does the time increase when it it not idle? Is there a be开发者_运维问答tter better approach to get the device idle time?