How Your Phone Knows Where You Are Without GPS
Indoors, your phone finds you by listening to nearby Wi-Fi routers and checking a map built by millions of phones.
The script
G P S can't reach inside most buildings... but your phone still knows which street you're on.
It's listening to Wi-Fi.
Every router nearby broadcasts a unique I D... even if you never connect.
Your phone collects them... and how loud each one is.
Then it asks a giant map: where are these routers?
You see, millions of phones built that map. Whenever one had G P S, it noted which routers it heard... and where.
Your neighbour's router is on it. Probably yours too.
Loud means close. Three or four routers... and it's found your street. So even though...
The facts, checked
- Wi-Fi positioning: phones scan nearby access points' BSSIDs (unique hardware IDs broadcast in beacons, even without connecting) and signal strengths, then query a location service.
- Google and Apple maintain crowdsourced access-point databases built from devices that report Wi-Fi scans alongside GPS fixes; Google lets owners opt a network out by adding "_nomap" to its name.
- GPS signals are weak indoors; Wi-Fi positioning typically gives roughly tens of metres of accuracy, enough for the street or building. Cell towers serve as a coarser fallback.
