This might work on piston guns too, I wouldn't know, I never got my piston to actuate, but I know that it works on my sprinkler valve. Holding down the blowgun trigger causes the gun to make a F# tone. I can adjust the pitch by putting my finger over the outlet on the blowgun. I have only got this to work once, but holding it down while filling it up and waving my hand at different distances from the outlet on the barrel, I can make it harmonic, where it gets very high pitched and much louder. I get different pitches with different barrels. Anyone else ever notice this?
Note: I live in a golf course neighborhood and the temptation to honk at people during down swing is growing stronger.