From CrunchGear:

Remember the X-ray technology from Total Recall? A British company has developed what it calls “ThruVision” — a similar technology that “uses what it calls ‘passive imaging technology’ to identify objects by the natural electromagnetic rays — known as Terahertz or T-rays — that they emit,” according to Reuters. “Depending on the material, the signature of the wave is different, so that explosives can be distinguished from a block of clay and cocaine is different from a bag of flour.”