. >> reporter: this is a map of waltham, massachusetts, and the red line is someone driving around theity. >> they ended there at b.j.'s wholesale is. >> reporter: that's pretty accurate. >> reporter: a team at northeastern university say they were able to track the driver's moves. it was just a test he's a recent doctoral graduate. >> secretly i am finding the location. >> reporter: but get this. he says they were able to find almost every twist and turn, even though the driver had his phone location turned off. would the user have any idea >> no idea at all. >> reporter: it's called a side channel attack because it targets sensors in your device that weren't designed to provide location like the accelerometers it measures like a gyroscope and magnetometer which works like a digital compass. a professor at northeastern university. >> they realize that their mobile phone with access to all these sensors is in some sense essentially you're looking at the best spying device you can imagine. >> reporter: and he says combining readings from the sensors could arm criminals with secret info.