But things are starting to change: at London’s Heathrow Airport, one of the world’s busiest airports, the dance is starting to fade. Thank technology: better imaging and software have pushed checkpoints from two-dimensional x-rays to computed tomography (CT) scanners that build a three-dimensional model of your bag. The 100-ml (3.4-ounce) maximum for carry-on liquids began in 2006 as a blunt response to a foiled transatlantic liquid explosives plot. The real upgrade is the algorithmThe real innovation in the new scanners, however, is the move to automated algorithms. The Transportation Security Administration is aggressively installing CT scanners at airports, but changing its policy is another matter—and any rule change will likely lag until CT is widespread enough to avoid patchwork protocols.