Why lost phones keep pointing at this Atlanta couple's home
Over the last year, more than a dozen people have shown up at Christina Lee and Michael Saba’s door in Atlanta looking for stolen smartphones. The visitors’ find-my-phone apps say their phones are inside the house, but they’re not. It’s been frustrating for Lee and Saba, not just because they fear someone angry and violent might show up one day, but because they didn’t know what was causing it.
Tech experts I consulted when I first wrote about Lee and Saba’s tech mystery were flummoxed. The phones included Androids and iPhones, on all the different carriers from Verizon to Sprint. But now security researcher Dave Maynor thinks he’s figured what’s causing this Bermuda tech triangle.
Maynor visited Lee and Saba’s home last week, accompanied by Reply All who I teamed up with to solve this tech mystery. He brought SDRs (software-defined radios) in order to scan for the signals and wireless access points in the area to see if there was a rogue cell tower that might be causing the issue. During the scans, he discovered something equally bizarre: on the mile-long street, he only detected nine wireless access points.
“In the five blocks around where I live by contrast,” said Maynor by phone, “there are 3000-4000 such devices.” (You can check out the density of devices in your own neighborhood on Wigle, a crowdsourced mapping tool.)
Lee and Saba live in a digital desert. Many of their neighbors are older, and some of the houses are not lived in, so their home is one of the few with a router.
That gave Maynor an idea about the root of their troubles. When phones attempt to geolocate themselves, they’ll usually look first to GPS or the cell towers they most recently connected to, but that won’t work if the phone is in a building without clear sight of satellites or if it’s off the cellular network. Then the phone will look to back-up location databases, first, using its IP address and, second, by looking at the nearest Wifi networks it can detect. Based on the signal strength of each Wifi connection, it can usually figure out within 10 meters where the phone is.
These IP and Wifi mapping databases are maintained by companies like Neustar, Maxmind and Skyhook, which have software embedded in millions of apps and phones, likely yours among them, that are constantly feeding them new, fresh mapping data—pairing the IP or Wifi networks the phone sees with GPS data. “Any time a location request is made on a phone we’re on, that information is used to recalibrate the system,” Skyhook’s chief technology officer Kipp Jones told me by phone.
As Reply All’s PJ Vogt put it in the episode about Lee and Saba’s home, “there’s databases feeding databases feeding databases.”
Maynor suspected the phones leading to Saba and Lee’s house might be deprived of GPS and cell tower triangulation, and so might be relying on IP address to figure out where they were, given that this particular area is low on wifi networks. “But looking at the IP address is not very specific; it’s just supposed to tell you whether the phone is in Atlanta or Zimbabwe,” said Maynor.