A stopper device is disclosed. The stopper device includes a substantially tubular support defining a first axis, and a tab extending along a second axis substantially perpendicular to the first axis. A cap is hinged to the support to pivot between a closed position and an open position. A tamper-proofing band is connected to the cap in its closed position via at least one breakable bridge situated along a third axis in a portion of the tamper-proofing band. The third axis is substantially perpendicular to the first and second axes when the cap is closed. The cap is pivoted from the closed position to the open position by squeezing along the third axis. During a first stage of the squeezing, the at least one breakable bridge is broken, and during a second stage of the squeezing after the first stage, the fastener tab disengages from the cap opening.