Your smartphone always knows where you are because it communicates with GPS satellites in space. But one day, perhaps, it won’t need that anymore. Instead, it may figure out your location using the effects of gravity on atoms right here on Earth, making it able to locate you even when you’re underwater, indoors, or underground.

The U.K.’s Ministry of Defense is investing “millions of pounds” in quantum location technology, the Financial Times reports. Such a “quantum compass” would be 1,000 times more accurate than any systems today and much more difficult to hack than GPS. Scientists working on the project told the Financial Times they expect to have a prototype in three to five years. If successful, the compass’ first applications would be in the military, including in super-accurate missiles, the New Scientist reports. Eventually, the technology could make its way into the civilian world.

Military and commercial engineers have long worked to come up with location-pinpointing that don’t depend on satellites. They’re trying to close some of the gaps in GPS’ abilities. One major gap: GPS signals are vulnerable to scrambling and spoofing. For the time being, at least, there’s no known way to interfere with a quantum compass, Bob Cockshott of the U.K.’s National Physical Laboratory told the Financial Times.

The quantum technology depends on trapping and cooling a “cloud of atoms” to just above absolute zero, the New Scientist reports. At that temperature, the atoms reach a quantum state that makes them especially sensitive to accelerations and even to the gravitational effects of the Earth. That means a quantum compass could measure where it’s going via accelerations. It could also determine its absolute location on Earth by comparing what it feels with a gravitational map of the Earth.

[Financial Times, New Scientist]