There's no code violation, because the sound a fire horn makes is not used exclusively for fire alarms (except, of course, for temporal code 3, which is a pattern, rather than a specific sound).
If you want proof, consider that there are such things as fire alarm bells. They sound remarkably similar to burglar alarm bells. There have been sounders intended for burglar alarm use that sound like fire horns, the main difference being that they weren't red. And System Sensor makes a fire alarm piezo horn that isn't even red. You just can't tell, either by sound or by color.
- badenov