Mini Air-Raid Siren

thingiverse

Based on the Orange Screamer, but modified to play two notes in a 5:6 ratio like an air-raid siren. The rotor has 6 fins on the bottom and 5 on top, which match the holes in the base and lid. There's a spiral air passage around the rotor, so air can flow around the rotor and into all the slots - my first version didn't have this and wouldn't spin. It's not super loud, but the tone is quite recognisable. You don't have to blow particularly hard to make a noise, but the noise stops as soon as you stop blowing. It's small enough to print without supports - the holes on the underside of the rotor are easily bridged. It takes about half an hour to print. Cad model is here: https://cad.onshape.com/documents/da45f3a75c78fdbb672b945b/w/24ad9ee3eb6304cac0a75c6e/e/19a2718f7886b45bcb4b525a