Cellphone tracking: Find an address? Easy. But new devices can calculate your altitude.

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 US 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. The systems, though now used mainly for apps that users control, are part of a new generation of location technology that could collect altitude data from smartphones and use it to, for example, help rescue crews find people trapped in an office-tower fire. But privacy advocates warn that detectives, intelligence agencies and maybe hackers could gain the ability to map the three-dimensional movements of cellphone users with startling new detail.

An early glimpse at this tension is playing out at the Federal Communications Commission, which is updating its requirements for how wireless carriers handle 911 calls, 70 percent of which now come from cellphones rather than land lines. In a proposal that could be adopted as soon as January, the FCC would require wireless carriers to build more-precise location systems capable of finding callers anywhere, even in a multistory building.