Ceiling Tiles
One time I was stopped by the head of security in the hallway of one of the buildings about how secure Kensington locks were, during the course of the discussion he informed me that someone had got into a locked office over the weekend, by getting into the unlocked office\lab next door lifting up the ceiling tiles to climb over the dividing wall & drop down to get the laptop of their desire.
They knew that was the MO as the individual did not clean his foot marks off the desks he landed on (unsure if he left the same way as he entered).