Usually, horns in a car are electric. The sound levels of these horns are about 109–112 decibels. They draw around 2.5–5 amperes of current. A car horn can honk for hours as it takes supply from the battery. A constant running car horn not only annoys the neighbours but also can drain your car's battery.
If the car horn keeps honking, it can be a failure in the switch or a relay failure. The best way to make the honking horn off quickly is to pull the horn fuse.