If you want to know when a user last opened his laptop at home then you can work with inventory but if you want to know if a laptop was shutted down then brought home and the next day docked then fired up you are fighting a loosing battle, no inventory will be able to tell you that since the laptop is shutted down.
In the second scenario the only not so perfect solution would be to use out of band technologies to detect that the laptop is still on it's docking station at night.