Subaru Forester: Instruments and controls / Horn

To sound the horn, push the horn pad.
Other information:
Before driving, adjust the inside rearview mirror so that you have a clear, centered view through the rear window. Making this adjustment before the vehicle begins moving helps ensure maximum rearward visibility.
Do not place luggage, cargo, or other objects in the rear seating area or cargo compartment if they obstruct your view through the rear window...
..