This is a simple design of a whistle. This one hasn't got a pea inside to help create the noise though. Instead, it uses a different mechanism to produce sound. As can be seen in the cutaway image, the whistle has a compression chamber at the beginning. When the air rushes in, it is forced through a very small opening, which increases it's speed. This fast moving air then swirls through the sound chamber and is interrupted by the incoming air. Finally, some of this air escapes through the angled sound hole at the top.

This whistle is reliable and will produce a very loud sound when blown. I havn't got the necessary equipment to measure sound, so if someone does, please post a make and let me know! The one I made was more than enough to fill the room with an authoritative sound!

Note: In order for the whistle to function at it's best, print with 3 walls and 70 percent fill for good strength, in addition to helping with the sound. The inlet, sound hole, and sound chamber must be completely clear and free of any strings for uninterrupted airflow. If not, stick a cotton swab into the sound hole to try to break up the stringing in the sound chamber. Fill the whistle with water and drain to remove the sediment.

There is also a version with a loop that can be used with a lanyard.