In future, Siri could shriek 'Help! Help', when someone tries to steal your iPhone from your pocket.
Apple's filed a patent for a method of detecting the sort of sneaky movements involved in theft by using the phone's accelerometer.
The patent, titled 'Acceleration-based theft detection system for portable electronic devices', doesn't go into a lot of detail about how to achieve 'theft detection'.
"Typically, theft or other large-scale movement of the device results in an acceleration signal having characteristics different from other events such as shock, impact, nearby machinery, etc," it reads.
"The detected acceleration as a function of time is thus analyzed to determine whether it corresponds to such large-scale movement of the device, rather than an innocuous event such as the impact of a book dropped nearby."
The system would also filter out non-suspicious movements, and the user would be able to control its sensitivity, picking their own level of paranoia. And if the phone does make a mistake, the user can input a code to calm it down.
Not all patent applications make it into reality - Apple files thousands every year - and this doesn't really seem like the best way of detecting theft. If your phone's in your bag, how will an accelerometer be able to tell if it's you removing it, or someone else? The company's other ideas on security, such as voiceprint, sound more sensible.