If you were protecting your smartphone passcode from someone lurking over your shoulder, or from unseen security cameras, you might cover the screen as you tap in the PIN’s four or six digits. But once you’ve unlocked the phone, perhaps you’d let down your guard, and leave the screen in full view—especially if it’s off.
That would be unwise, according to researchers at two German universities. At an upcoming conference on human-computer interactions, they will present a new study that explains how someone armed with a thermal-imaging camera would have little trouble extracting your passcode from the heat signature left on your smartphone’s screen. It even works 30 seconds after you last touched it.
