Abstract: A magnetomechanical EAS marker includes a housing, a magnetostrictive active element in the housing, and a bias magnet mounted on the housing adjacent to the active element. Both the active element and the bias magnet are substantially planar metal strips. The length and/or surface area of the bias magnet is substantially less than the length and/or surface area of the active element. The reduction in the size of the bias magnet relative to the active element enhances reliable deactivation of the marker by increasing the resonant frequency shift obtained by degaussing the bias magnet. The increased reliability of deactivation is obtained without increasing the sensitivity of the marker, when in an active state, to variations in applied bias magnetic field.