An Explanation of Wi-Fi Triangulation

Wi-Fi Positioning System (WPS) is a geolocation system that relies on Wi-Fi to locate compatible devices and users. Wi-Fi often works alongside GPS to improve accuracy. Companies like Google, Apple, and Microsoft use GPS to identify Wi-Fi networks, which can then be used to find someone's device as it relates to nearby Wi-Fi.

Wi-Fi positioning is useful in urban environments, where there are many wireless networks broadcasting within the same area. It is also useful in places that are out of reach to GPS, such as tunnels, large buildings, and underground structures.

However, WPS does not work when out of range of a Wi-Fi signal; if there aren't any Wi-Fi networks around, then WPS will not work.

How Wi-Fi Location Services Work

Devices that have both GPS and Wi-Fi can be used to send information about a network's location back to a GPS service. The GPS device transmits the service set or "BSSID" (MAC address) of the access point along with the location determined by GPS.

When GPS is used to determine the location of a device, it also scans nearby networks for publicly accessible information that can be used to identify the network. Once the location and nearby networks are found, the information is recorded online.

The next time someone is near one of those networks but does not have great GPS signal, the service can be used to determine an approximate location since the network's location is known.

Let's say, for example, you have full GPS access and your Wi-Fi is turned on in a grocery store. The location of the store is easily spotted because your GPS is working, so your location and some information about any nearby Wi-Fi networks are sent to the vendor (such as Google or Apple).

Later, someone else enters the grocery store with Wi-Fi on but, because there's a storm outside, they have no GPS signal. Their location can still be determined thanks to Wi-Fi network positioning. Vendors like Microsoft, Apple, and Google are always refreshing this data, using it to provide more accurate location services to users. And it is disclosed involuntarily; vendors do not need Wi-Fi passwords to locate contributing networks.

Anonymously determining user locations is part of virtually every cell phone carrier's terms-of-service, though most phones allow the user to turn off location services. Similarly, if you don't want your own wireless network to be used in this way, you may be able to opt out.

Opt out of Wi-Fi Tracking

Google includes a way for Wi-Fi access point administrators to opt out of its WPS database. Simply add _nomap to the end of the network name (e.g. mynetwork_nomap) and Google will no longer map it.