Toyota PRIUS Manual page 199

 System maintenance
The vehicle has a maintenance-free type alarm system.
 Items to check before locking the vehicle
To prevent unexpected triggering of the alarm and vehicle theft, make sure
of the following:
 Nobody is in the vehicle.
 The windows is closed before the alarm is set.
No valuables or other personal items are left in the vehicle.

Triggering of the alarm

The alarm may be triggered in the following situations.
(Stopping the alarm deactivates the alarm system.)
PRIUS PHV_OM_OM47831E_(EE)
The doors are unlocked using the

mechanical key.
 A person inside the vehicle opens a
door, the back door or hood.
 The 12-volt battery is recharged or
replaced when the vehicle is locked.
(P. 622)
1-8. Theft deterrent system
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