Attaching a tracking unit to every painting might sound like a no-brainer, but it’s actually a huge challenge, Wittman explains. You’d need something that has a long battery life that you don’t have to constantly be charging. It would have to be small, small enough to put on the piece without damaging it and small enough to evade detection by thieves. At the same time, it would have to be designed so that if thieves did find it, they could remove it without damaging the art. This mythical unit would have to be powerful enough to transmit from inside boxes and closets and warehouses where burglars might take it, but cheap enough to allow museums to buy thousands of them. “That technology simply doesn’t exist,” Wittman said.

That’s not to say that people aren’t working on high-tech solutions to art protection. In recent years RFID technology—using electromagnetic fields to identify and track tags on objects—has become more common in museums. In these setups, art is fixed with a small RFID tag that detects if the piece of art moves from its location on the wall or floor. An RFID reader in the building keeps track of these locations. So if someone pulls a painting off a wall, the alarm goes off immediately. But RFID systems only work inside the building. The tracker can only keep tabs on tags within about 230 feet. Once that painting is out the door, it’s electromagnetically invisible.

And Wittman points out that if the rest of your security isn’t good, RFID isn’t going to help you. “If you have a situation where four individuals go in with machine guns, they don’t care about the RFID. Everybody knows they’re there with the machine guns.” And in situations where thieves are efficient, knowing that a piece of art is moving once the thief has it off the wall isn’t useful. In one case in the Kunsthistorisches Museum in Vienna, a thief broke through a window and a display case and made off with a sculpture known as the Cellini Salt Cellar in just 58 seconds. No alarm response system can react that fast.

Steve Layne, the founding director of the International Foundation for Cultural Property Protection, says that museums would rather focus on arming the environment than the piece of art itself. “Curators don’t like anything affixed to artwork,” he told me. Instead, Layne says that that most museums put their effort on making sure the art doesn’t leave the museum in the first place. “The primary focus is not on tracking art outside the museum, it’s on tracking it while it’s in the museum,” he said. “The emphasis is on stopping anything from leaving the walls.”

Museums don’t like to disclose what they do and don’t use for security. Neither the Museum of Modern Art nor the American Museum of Natural History would tell me anything about the types of security features they have on individual pieces.