People have used magnetic compasses to find their way outdoors for centuries. In a twist, a startup has found a way to use the magnetic sensors in smartphones to locate people themselves—this time, indoors, where GPS signals don’t normally reach. Tracking people in this way could lead to mobile maps that work indoors, and let stores target offers to customers standing in front of a particular product.

The Finland-based startup, Indoor Atlas, launched last week as spin-off from the University of Oulu. The company’s technology, intended for mobile software developers to use in other apps, is a new approach in the growing market for systems that track people inside.

The company says its method pinpoints people more accurately than many current methods, which typically employ the Wi-Fi or radio signals detected by a smartphone and are precise to within several meters. Indoor Atlas says its approach is accurate to between 10 centimeters and two meters, depending on the building. That’s the difference between, say, knowing a shopper is in the freezer section versus knowing he is standing in front of the ice cream. It also does not require a building to have any special equipment.

The market for indoor location technologies is beginning to explode (see “The Indoor Positioning System Era”). Google Maps first launched an indoor “My Location” feature last November, partnering with large retailers, airports, and now museums to upload floor plans. Other companies, such as Nokia and chip maker Broadcom, are also developing their own technologies, and Apple and Microsoft are following Google’s indoor mapping endeavor. Bruce Krulwich, a mobile industry analyst at Grizzly Analytics, has tracked at least 40 startups focused on indoor positioning globally, and IMS Research predicts there will be at least 120,000 indoor venue maps available to consumers by 2016 (see “Bringing Cell-Phone Location-Sensing Indoors,” and “Using Wi-Fi for Navigating the Great Indoors”).

Indoor Atlas’s technology works by analyzing the magnetic field inside a building. The structure of a building causes disturbances to the Earth’s magnetic field. Once these disturbances are mapped, people can be pinpointed within them through their phone’s magnetometer. Indoor Atlas’s product arose from research findings that showed the signature magnetic field within buildings was sufficiently varied and stable to be used for navigation, says company founder and computer science professor Janne Haverinen.

To use the technology, a developer would upload a building floor plan to Indoor Atlas’s servers, and then create a magnetic map of the area by walking around with the company’s smartphone tool. He or she could then build an app that communicates with Indoor Atlas’s cloud-based servers to pinpoint user locations.

Krulwich says the requirement for such preparations would deter Google, Microsoft, or Apple from ever using such a technology—they will stick with options such as Wi-Fi, which works immediately as long as a signal is available. But, he says, Indoor Atlas’s technology could appeal to thousands of other more niche application developers who want to track locations at specific places.

“It is difficult to predict the killer application,” says Indoor Atlas’s Haverinen, who, after developing the research and business plan over the past year, has raised seed funding from Helsinki-based business accelerator KoppiCatch. Now he’s reaching out to developers in an attempt to attract early adopters.