In order to design a safety device (51) for a seat (42) for a vehicle, in particular motor vehicle, with an at least partially flexible seat surface (1) and with a barrier means (2) which is to be arranged essentially under the seat surface (1) and is to be erected, in particular in the event of an accident, to prevent an occupant from being displaced forwards in the direction of inertia (3), such that the occupant is securely held in the seat even in the event of an accident, it is proposed that the barrier means (2) is held in the erected state (4) by means of a holding means which is held essentially in a manner such that it does not move back out of a final state corresponding to the erected state (4) of the barrier means (2) without an additional application of force, wherein the holding means is, in particular, a self-locking means (5) and/or a ramp means (43) Which can be latched in place.