 <p>The Skyhook system seems to work only for mobile devices. It uses either GPS (from the device's own GPS software), knowledge of the location of the WiFi access point in use, or triangulation from the cell towers that are in use.</p> <p>Details are <a href="http://www.skyhookwireless.com/howitworks/" rel="nofollow noreferrer">here</a>.</p> <p>The best accuracy comes if the user is willing to share their GPS location, or their WiFi access point is listed in the Skyhook database. However, most casual users won't have their GPS antenna turned on unless they're navigating somewhere, and most private or corporate WiFi access points won't be listed.</p> <p>So in practice this service is only really useful for applications where the user gives consent, such as tracking devices in use by a company. </p> <p>The fallback is to use geolocation of the IP, which as I mentioned in my comment above is very very inaccurate and is really only of use for fun.</p>