Autonomous device (10) comprising a first plate (21) having a first surface (210), a second plate (22) having a second surface (220), and an elastic mechanism (30) for bringing the first (210) and second (220) surfaces closer together and for placing a pouch (40) able to contain a fluid under pressure between said surfaces, the autonomous device (10) being configured in such a way that said first surface (210) and said second surface (220) are able to face one another, and being characterized in that said second surface (220) of the second plate (22) is convex from a viewpoint (35) situated between said first (210) and second (220) surfaces of the first (21) and second (22) plates.
