Check if laptop in use?

[Jacob S <stormspotter@6Texans.net>]

I have a laptop on my network that I need to do an occasional upgrade
on. It runs Debian - what else? :-) I'd like to make sure it's not
currently in use when I do the upgrades though, as the upgrades are
usually done over the network via ssh.

I know this user always closes the lid on their laptop when they leave
it for any extended period of time. So, my question is, is there a way
to check the status of the lcd screen/lid closed switch? Alternative
suggestions that would work better?

I would check running processes, but they know the power of Linux and
always leave it logged in while they're gone, with a couple dozen
processes open, etc. I could check cpu idle time, but cron can make it
busy and text editors don't have a very big footprint once the file's
open.

Any tips would be appreciated.

TIA,
Jacob