A mechanical warning device (1) for a vehicle, including for a velocipede, includes a body (2), a ringer (3) mounted on the body, a striker (4) movably mounted on the body and relative to the ringer, and a magnet mechanism (5) which is configured such that, when the striker is displaced from a stable position to an intermediate position in which it has been displaced away from the ringer, it drives the striker from the intermediate position to strike the ringer then brings the striker back into the stable position.