Horn, signal
Source Advanced Player’s Guide
Sounding a horn requires a DC 10 Perform (wind instruments) check and can convey concepts such as Attack!, Help!, Advance!, Retreat!, Fire!,
and, Alarm! The report of a signal horn can be clearly heard (Perception DC 0) up to a half-mile distant. For each quarter-mile beyond, Perception checks to hear the horn suffer a 1 penalty.