Skyhook located phones with Wi-Fi it never installed, beating GPS indoors

GPS locates a phone outside, but not indoors, underground or between tall buildings. Cell-tower triangulation is coarse, and deploying dedicated location beacons everywhere was uneconomical.

Skyhook's idea, published as Place Lab with Intel Research in 2005, was to treat the Wi-Fi access points and GSM towers already in the environment as landmarks: build a database of their positions and let the device locate itself by the beacons it hears. Experiments in the Seattle area showed 20–30 meter median accuracy with nearly 100% daily coverage.

In 2007 Apple licensed the technology and added it to the iPhone and iPod touch in 2008 — solving the iPod touch's missing-GPS problem. Skyhook held more than 100 patents and also served Sony and AOL's MapQuest; when Google launched Wi-Fi navigation in Android in 2010, Skyhook sued over its patents.

Use beacons that already exist everywhere

Wi-Fi access points are ubiquitous and their signals are stable landmarks.

A cached beacon database means no network connection is needed to locate.

Mapping the beacons was one-time effort with lasting value.

It worked precisely where GPS failed: indoors and in dense cities.

Don't build the sensor network — read the one that already exists: your product can borrow infrastructure (radio beacons, stores, cars) that someone else paid to deploy, as long as you map it first.

Apple replaced Skyhook with its own Wi-Fi positioning by 2010, and Skyhook's patent suits against Google ran for years. But the idea won: Wi-Fi positioning is now standard in every smartphone, and indoor location remains a core feature of mobile maps.