Seat Leon Owner's Manual page 21

20 Seat belts
After the ignition has been switched on, the control lamp  on the instru-
1)
ment panel lights up if the driver has not fastened his/her seat belt, and
an audible warning is heard if the vehicle is driven at more than 30 km/h
(20 mph).
The warning lamp*  is switched off if the driver seat belt is fastened while
the ignition is switched on.
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1)
Depending on the model version