Abstract: Device (1, 2, 3, 4) for warning of the under-inflation of a tire, mounted the wheel of the tire, includes a stationary element (10, 71) with two inner chambers (11, 12, 73, 74), one (11, 73) of which is brought to the inflation pressure, the other (12, 74) to the atmospheric pressure, and a centrifugal mass (20, 72). A blocking device (30, 90) blocks any displacement of centrifugal mass (20, 72) when the inflation pressure is greater than a certain threshold and frees the centrifugal mass (20, 72) when the inflation pressure decreases below the inflation threshold. Centrifugal mass (20, 72) can then become off-centered under the effect of centrifugal forces and creates a dynamic imbalance able to be sensed by the driver of the vehicle.