The access points themselves listen for the Wi-Fi signals created by your phone, then estimate its position via trilateration.

FORBES: Smartphone Location Tools Are Great ... Until You Get to the Front Door

Loran requires three singles, with locations then calculated through "trilateration".

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However, all modern smartphones have Wi-Fi built in, and wireless networks are common enough in indoor spaces that an app could easily scan for known access points and calculate your position using trilateration.

FORBES: Smartphone Location Tools Are Great ... Until You Get to the Front Door