factory alarms

I have a 2000 Grand Prix GT, does anyone know why once a day the horn toots 3 times for no apparent reason. Is there some kind of electrical failure going on that trips the factory alarm?

Does this happen when something loud goes by like a truck or motorcycle? The shock sensor may be set to sensitive. My horn would sound when a loud vehicle went by until I adjusted the sensitivity down a notch.

I know the new Silverados sometimes will do that when you start it when it's real cold. It has to do something with the battery being real low or something.