Still, it could be very useful for intelligence agencies. If they have identified that a phone is being used by a terrorist they can identify which terrorist is

Still, it could be very useful for intelligence agencies. If they have identified that a phone is being used by a terrorist they can identify which terrorist is carrying it if they're able to get access to its accelerometer. Or they could gain access to millions of phones' accelerometers and identify which ones are being used by known terrorists. At the very least I expect to see it in some spy movies in the next few years.