A device for ensuring that two sheet pile locks (10, 12) are hooked correctly, comprising a detector (18) which is arranged in the locking area (14) of the first lock in such a way that a complementary lock part (16) of the second lock crosses through said detector when the sheet pile locks are hooked correctly. The inventive device also comprises an electric circuit which determines when the detector (18) has been crossed through. The electric circuit comprises a mounting (28) inside the detector. Said mounting has a first impedance value prior to the through-crossing of said detector (18) and a second impedance value after through-crossing has occurred. Both impedance values are distinctly different from the impedance value of a short circuit or an interruption in the electric circuit outside the mounting.