He dialed Securilink, the vault's alarm company.
"What is the status of the alarm?" he asked.
"Fully functional," the operator said, checking the signals coming in from the Diamond Center. "The vault is secure."
"Then how is it that the door is wide open and I'm standing inside the vault?" De Bruycker demanded, glancing at the devastation all around him.
A security camera recorded his movements—police would later watch the footage—but the guard had gotten used to the Italian's frequent visits and wasn't paying attention. Notarbartolo stepped away from the safe-deposit boxes and pulled out the aerosol can. With a quick, practiced circular movement, he covered the combined heat/motion sensor with a thin coat of transparent, oily mist.
The vault was momentarily filled with the smell of a woman's hair.
It was a simple but effective hack: The oily film would temporarily insulate the sensor from fluctuations in the room's temperature, and the alarm went off only if it sensed both heat and motion.
That’s from a story in Wired about a huge diamond heist. You can read it here.