Toyota prius Owner's Manual page 77

 Effective range (areas within which the electronic key is
detected)
Vehicles with entry function of driver's door
PRIUS_OM_OM47871E_(EE)
1-3. Opening, closing and locking the doors
When locking or unlocking
the door
The system can be operated
when the electronic key is
within about 0.7 m (2.3 ft.) of
driver's door handle.
When starting the hybrid
system or changing
"POWER" switch modes
The system can be operated
when the electronic key is
inside the vehicle.
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