I’m not, in general, a big fan of noise but here’s a possible exception.
Lots of cyclists are involved in accidents and often it’s because neither car drivers nor pedestrians can hear them coming.
Today’s invention is simply to attach a light plastic tube to some of the spokes of a bicycle’s front wheel. Each tube would be mounted parallel to its spoke with the end closer to the axle closed off. As the bike moves down the street, air rushing over the open end of a pipe causes it to hum, just like blowing over the lip of a beer bottle.
Rotation of the wheel would cause an increase and decrease in volume from any one tube, corresponding to the 12 or 3 o’clock positions, for example.
The tubes could be of different lengths and even tuned in order to generate interesting, even personalised chords. This effect could be enhanced by locating the tubes in a range of circumferential positions.
As the bike’s speed increases, so the frequency of the ‘siren’ would increase. This provides other road users with an extra indication that a bicycyle is closer than they thought and also gives an indication of the speed at which it’s travelling.