The invention relates to means for sealing measuring instruments and equipment, specifically to seals with a blockable rotor to enable monitoring for unauthorized access to instruments measuring consumption of electrical and heating energy, natural gas and water. A seal with a rotor comprises a transparent body (1) made from a high-strength plastic and formed with a cylindrical cavity (2) having a blind end and openings (3) which are formed on lateral sides of the cavity (2) and through which a flexible sealing element passes, and a rectangular cavity (4) which is installed at the open end of the cavity (2), transversely with respect to the latter, wherein the cavities (2) and (4) are interconnected. A rotor (6) is arranged in the cavity (2) so as to be rotatable in one direction. Openings for the flexible sealing element are formed in the lateral walls of the cavity (2) and in the rotor. A cross-shaped blocking element (9) is installed at one end of the rotor. A device (5) for blocking the rotation of the rotor is arranged in the cavity (4), one end of which device is provided with two projections in the form of a fork (13), between which a trapezoidal groove (15) is formed for securing the cross-shaped blocking element (9).