The invention relates to a unit for molding containers, which comprises two mold supports, a device for locking the mold supports in the closed position, and a bistable device which comprises a fixed element and a mobile element able to move between two stable extreme positions. The mobile element comprises a mobile magnetic dipole, and the fixed element comprises a fixed magnetic dipole, the fixed magnetic dipole applying a magnetic force from a distance to the mobile magnetic dipole in order to force the mobile element toward one or other of its two stable extreme positions.