Can be check when user system is locked and when it again unlocked

[callashwini]

Can be check when user system is locked and when it again unlocked using window services?

I am trying to make a application which will check how many hour user work on the sytem, currently i am able to get the time between start and shutdown. But also want to get the detail how much time user system is locked or how much user spend actively.

Thanks
Ashu