Cellphones long have doubled as tracking devices, capable of revealing your location to police, paramedics, even grocery stores looking to deliver coupons to nearby customers. But there’s a measurement cellphones once struggled to make: altitude.
No more.
Cellphone tracking is about to go vertical as the location-services industry, prodded by the U.S. government, solves the riddle of what experts call “the z vector.” Soon it will be possible to determine not only what building you and your phone are in but also whether you are on the first or 15th floor.
One key is the rapid spread of barometric-pressure sensors, which have become standard features in Apple’s iPhone 6 and several Android devices. More than 100 million of these smartphones already are in the hands of consumers, capable of making air-pressure readings that can be used to estimate a user’s altitude, to within a few feet.
