For completeness, Here is a link to the tesla manual I find online when I google "tesla model 3 manual". Its dated october of 2020, so might be slightly out of date, but will definitely work for most things (including this inquiry):
The text on page 11 that is referenced by
@TBrownTX , is as follows (bold and emphasis mine)
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Passive Key Fob Due market region or vehicle configuration, Passive Key Fob may not be available for your vehicle. Locking and unlocking Model 3 with your key fob is conveniently hands-free. Although you must be carrying a paired key fob, there is no need to use it.
Model 3 has sensors around the vehicle that can recognize the presence of a key fob within a range of approximately three feet (one meter). Therefore, you can keep your key fob in your pocket or purse and simply pull on the door handle to unlock. When carrying your key fob with you, you can also open the trunk without having to use the key by pressing the trunk's exterior door handle.
If Walk-Away Lock is on, your vehicle automatically locks when you exit and senses that the key fob is no longer in range (see WalkAway Door Lock on page 14). Passive key fob is automatically enabled when you pair your key fob to your vehicle.
The key fob can only be paired to one vehicle at a time. If you want your key fob to passively lock and unlock for a different vehicle, touch the flat side of the key fob onto the driver's side door pillar or center console card reader.
You only need to do this once to pair it to your desired vehicle. You must pair your key fob every time you use it with a different vehicle. NOTE: Only key fobs with the TESLA logo printed on the flat side have the passive locking and unlocking functionality.
Key fobs with the MODEL 3 logo printed on the flat side cannot passively lock and unlock your vehicle. NOTE: For increased security, your key fob disables itself after five minutes of being stationary while in range but the vehicle is not in use. The vehicle will not lock or unlock passively when this occurs. Shake or press a button on your key fob to wake it up.