A fuel efficiency signal device intended to be interposed between the accelerator pedal of a vehicle and a floor below the pedal. The signal device has wedge shaped, flexible walled, self supporting air container having walls sealingly blended to adjacent walls to form the air container. The walls are a bottom wall, a fore end wall extending upwardly from the bottom wall and formed with a lateral, inwardly extending living hinge, an aft end wall extending upwardly from the bottom wall, a pair of opposite, outwardly bowed side walls extending upwardly from the bottom wall and joined to the end walls and a top wall inclined at a wedge angle to the bottom wall and joining the side walls and the end walls. A whistle extends through a wall of the air container. An adjustable air escape valve also extends through a wall of the air container device for adjustably varying the air flow rate through the air escape valve and thereby adjustably selecting a rate of accelerator pedal depression at which the whistle will emit an audible signal to the driver.