Ancient Greece: Herons Trumpet Signal

For the use in temples, Heron proposes following construction in his 'Pneumatic':
A rope is mounted on the door of the temple, which pulls a lever. This lever pushes a hemisphere into a water jar. The water presses air into the hemisphere. This air will now float through a trumpet, which is mounted on the hemisphere. A tone is created by pressure.
If the door is closed, the lever falls back to its first position. The hemisphere lifts and air will float into it.