[nooloop]

That might be overly simplistic. The three issues I see are:

1) Company hardware. Don't use theirs since it's unethical without permission, and even with permission, your employment contract might give them rights to your work.

2) Time. Just because you're in the office doesn't mean you are on their time, but if you are, then that's unethical too.

3) Space. If you've satisfied the first two conditions, it seems like little harm is done and little risk assumed by working on your own laptop on your own time while in the office.

Lastly, I'd worry more about network monitoring than keystroke loggers. If you attach your laptop to their network, you're still using their company resources to do your work.