These horns always come in identical pairs, one of which is quite useful, while the other is cursed. Known properly as Anchored Signal Horns, these items radiate powerful magic if tested for, but no amount of testing will reveal a cursed from a non-cursed one. They can be plain, or ornately worked, and are usually made from the horn of a bull, buffalo, or other powerful animal or creature. The horn will radiate strong magic, if tested for.
Each horn is magically locked to a specific place, usually one particular corner of a castle wall, or perhaps the watchtower of a fort, or even the throne room of a king. The wielder of the horn can travel anywhere, no matter how far, even across planes of existence, and, if they sound the horn, it will also be heard in this anchored location.
Usually used in conjunction with sounding codes ("Three long blasts, and two short, mean the enemy is on the march."), the cursed version of this item deliberately relays the wrong signal. No matter what code is agreed upon, the Treacherous Horn will sound off the worst or most confusing signal possible under the circumstances, up to and including no signal at all -- whatever can bring about the most negative situation. Unfortunately, Anchored Horns are linked to each other. Attempting to make a distinguishing mark on one causes an identical mark to appear on the other. Destroying or damaging one does the same to the other, no matter how distant they may be.
A Treacherous Horn is usually hidden away in some secret location, while its counterpart is used by elite scouts, spies, or armies in the field. A few have been forgotten, and occasionally, enemies of a kingdom have specifically sought out Treacherous Horns for use in elaborate invasion plans.