The System Sensor H12/24 Selectable Output Horn operates on either 12V or 24V. Mounts to a standard 4˝ × 4˝ × 11/2˝ back box or a single gang 2˝ × 4˝ × 17/8˝ back box using the universal mounting plate (included).
Came in perfect condition. Works well and is loud. The only downside is the removal tool is plastic and tends to bend while using it. However, it does do the job of removing the wall cover.