Detect that keyboard was disconnected overnight

"It should depend on the machine, but my guess would simply be no.

When you disconnect and reconnect the keyboard or mouse of some older machines, they are not automatically recognised and will not function until you reboot.

With newer machine, it appears that there is no ""Intelligence"" in the port (although they are better... so intelligence is a weird word), they are just always active if a keyboard is in or not, so I just do not think there is a programmatic way anyone can query or see if the keyboard is connected.

Your best bet will simply to be to look at the back of the machine and check there isn't an unknown device there."

The keyboard logger could be a passive device. Try putting your AM radio next to the keyboard.