How the Tesla Model 3 Works without a Key or a Fob – Car and Driver (blog)
Car and Driver (blog)
The Model 3 uses a technology called Bluetooth Low Energy (or LE) that is built into most smartphones made in the past few years (and every iPhone since the iPhone 4S). It allows for a low-power, always-on connection between the phone and the car.
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Source:: Bluetooth Low Energy