A few years ago, there was a marked shift in video games that few but the most ardent gamers probably noticed. It was such a good idea that it seemed to appear in every game overnight, no matter the publisher or platform.

Rather than simply displaying a map and expecting you to navigate a level (leading to a lot of pausing and cursing), AI began tracking your position, calculating where to go in real time. The kicker? The proper path simply glowed in front of you as the ultimate, personalized GPS.

Guiding Light, by MIT Media Lab Research Assistant Jaewoo Chung, is the exact same idea, but applied to real life and completely functional where most GPS units fail: indoors. Using a smartphone with a mini-projector and magnetic positioning, Guiding Light projects an arrow on the ground that points the direction to anywhere you want to go. Gorgeous, it’s not. But the utilitarian prototype is clear and easy to use.

“I wanted to create an augmented reality system that provides guidance without getting your eyes distracted by small screens such as mobile phone screens,” says Chung. “I was inspired by the typical use of a flashlight–we hold it in our hands to reveal objects that we illuminate.”

Imagine never getting lost in a mall or museum again.

As most of us have already replaced our flashlights with flashlight apps, the smartphone was a perfect platform for Chung’s vision. But the real technology that makes the idea possible is its magnetic tracking. GPS doesn’t work indoors, Wi-Fi triangulation can’t figure out which way someone is facing, and compasses–the oldest yet most promising technology–are thrown off by a building’s magnetically augmenting steel infrastructure. “This distortion results in errors such that the e-compass doesn’t point to the magnetic north,” says Chung.

But one of the same principles that made magnetic tracking impossible would enable Chung’s team to solve the problem. Rather than be thwarted by each building’s unique and confounding magnetic fields, they’d exploit that phenomenon for their own use. Using a Bluetooth badge equipped with four magnetic sensor arrays, Guiding Light positions a user within the thumbprint magnetic fields of any given building. It requires no special infrastructure, though each building needs to be “magnetically mapped” first.

Technology aside, the basic directional interface behind Guiding Light could be used in a lot of scenarios. Imagine never getting lost in a mall or museum again, or always knowing the nearest exit in case of a fire. The only real question is, will pocket projectors or augmented reality lenses take off first?