When one’s tyre treads wear down towards the legal limit, it’s not always obvious (until you end up parked in a hedge perhaps).
Today’s invention is a way to become aware of this problem in advance of a terminal loss of traction.
A band of hard plastic would be inserted, during manufacture, in one of the circumferential tread gaps. This would eventually be exposed to the road surface as the surrounding rubber wears away. When this occurs, serrations in the surface of the plastic make a characteristic buzzing noise as the wheels rub on the road.
This would be annoying enough for people to find it necessary to visit a garage quickly to buy new tyres. The noise might even be made to increase and decrease in frequency, in a siren-like way as the wheel in question rotates.