[The World’s Biggest Diamond Heist(https://www.wired.com/2009/03/ff-diamonds-2/)

These guys managed to blow through many layers of hi-tech security with careful planning and some low-tech tricks, and one huge security gaff: the “unduplicatable” key for the vault was hung on the wall in a storeroom next door.

My favorite bit, I think, was how they disabled a magnetic sensor on the vault door, that would detect the door being opened; they brought a piece of aluminum covered in double-sided tape, stuck it over the sensor pieces, unscrewed the pieces from the vault door and door frame, and swung them out of the way. The sensor was never triggered because the two pieces remained in contact…

The article is a bit long, but it’s worth reading both for how they got through all of the security, and the one stupid mistake they made that led to them all getting caught…