Observe a demonstration of a Rotator Siren from the Physical Science Collection at the Smithsonian's National Museum of American History.This is about as simple a siren as it is possible to build. It's basically a single metal disk with two rows of evenly spaced holes. Here it is mounted on a "Rotator", a pulley device once common in American classrooms. In this demonstration, as one student cranked the rotator the disk would start spinning rapidly. A second student would then blow air through the holes with a flexible rubber tube. The faster the first student cranked, the higher the tone. The harder the second student blew through the tube, the louder the sound. Although the sounds this apparatus produced were not musical, this was an effective (and inexpensive) device for demonstrating basic acoustic principles.