LIKE the trail of crumbs in the tale of Hansel and Gretel, data trickling from the gadgets we carry in our handbags and pockets map our every move. By adding GPS readings to output from the motion sensors that are becoming increasingly common in cellphones, it is possible to build up a meticulous record of an individual鈥檚 day-to-day activity.
This can now be exploited by apps on the phone to predict what services we will require or to spot abnormal activity that could indicate we need help (see 鈥淢otion-sensing phones that predict your every move鈥�). Yet just as Hansel鈥檚 breadcrumb trail failed to save the pair when birds ate it, its modern equivalent could go equally badly wrong. The data smartphones generate must remain under their owners鈥� control, and not be hijacked by advertisers or other self-interested third parties.