Wi-Fi-Derived Location Information and User Device Tracking

How Wi-Fi Provides Precise User Location Data

1. Wi-Fi–Derived Location Information Can Provide Law Enforcement with Precise and Voluminous User Location Data.

Because of the way that devices like cell phones, tablets, and laptops connect to wireless Internet networks, those devices generate precise information about users’ current or historical locations. When these kinds of Wi-Fi networks are operated by entities like colleges, businesses, or city governments, those entities thereby obtain a log of location information about any user accessing them This information, often timestamped down to the second, provides a detailed picture of where a given Wi-Fi user has been in space and time.

2. Wi-Fi Networks Collect User Devices’ Information as They Connect to the Internet. 

An overwhelming majority of Americans now own smartphones and connect these phones to Wi-Fi networks in their homes, offices, and in public spaces to browse the Web, connect with friends over social media, play games, and send text messages or e-mail.4 Wi-Fi networks use radio technology to connect user devices like cell phones, tablets, and laptops to physical devices called Wi-Fi “access points,” which in turn connect to the Internet.5 The radio contained within each phone, laptop, or other device is manufactured with a unique identifier called a “MAC address,” which is a code made up of letters and numbers.6 Access points use these unique codes to identify and log information about which devices are communicating with them at any given time.

3. Wi-Fi Networks Can Log Device Locations as Their Users MoveThroughout Physical Space. 

Wi-Fi networks can be used to track users’ location and movements through physical space. Because network administrators know where access points are physically located within a Wi-Fi network, and because networks log the exact time and date each device connected to each access point, administrators also know that the devices connecting to those access points are in the nearby vicinity and know when they connected. While a home network may rely on only a single access point, a larger network—covering an office building, college campus, neighborhood, or even an entire city—must deploy multiple access points to ensure users’ seamless connections to the Internet.

That is because the typical range of a Wi-Fi access point is approximately a few hundred feet, under perfect conditions.8 Additional access points are necessary in larger geographic areas, as well as in dense indoor areas, like offices or dormitories, because heavy materials like concrete, cinder block, and brick can block Wi-Fi radio waves.9 Further, each access point can only support a limited number of devices, so a network supporting a large number of devices, as in a college dorm, requires many access points to avoid congestion.

The more access points a network has within its geographic area, the more detailed and specific the location information it can generate. In this case, Moravian densely blanketed the campus, an area spanning about six blocks, with over  access points to ensure students receive signal anywhere on campus. (R.R. 51a.) The College placed access points in classrooms and dining halls, as well as outside buildings—basically, “anywhere a human being who wants to access the wireless [I]nternet will be,” (R.R. 54a), including up to eighty to ninety access points each in certain residence halls, yielding one access point for approximately every other dorm room