An overspeed emergency brake system for elevator cars, comprising an overspeed detector magnet generating a brake actuation force and a kinematic constraint element guiding movement of the overspeed detector magnet with respect to a reaction surface, characterized in that; the overspeed detector magnet, the reaction surface and the kinematic constraint element are arranged such that; the kinematic constraint element is attached to the elevator car for defining the motion of the overspeed detector magnet with respect to the elevator car and the reaction surface; - a linear brake actuation force is generated at a normal operating speed condition due to the movement of the overspeed detector magnet along the reaction surface; the overspeed detector magnet and the reaction surface are linked with a magnetic force where a surface of the overspeed detector magnet partially overlaps with the reaction surface, or excitation rate caused by a periodic feature of the reaction surface is out of a resonant region of the kinematic constraint element and the overspeed detector magnet; and - the kinematic constraint element converts the linear speed-force relationship into a nonlinear speed-force relationship in an overspeed condition, while generating a sharply increasing force for triggering the overspeed emergency brake; where the overspeed detector magnet is translated with respect to the kinematic constraint element or the overspeed detector magnet is moved across the reaction surface due to the kinematic constraint element whereby the surface of the overspeed detector magnet is completely overlapped with the reaction surface, or where the kinematic constraint element is started to resonate at an amplitude which triggers the overspeed emergency brake by modulating the brake actuation force by a periodic feature. - a linear brake actuation force is generated at a normal operating speed condition due to the movement of the overspeed detector magnet along the reaction surface; the overspeed detector magnet and the reaction surface are linked with a magnetic force where a surface of the overspeed detector magnet partially overlaps with the reaction surface, or excitation rate caused by a periodic feature of the reaction surface is out of a resonant region of the kinematic constraint element and the overspeed detector magnet; and - the kinematic constraint element converts the linear speed-force relationship into a nonlinear speed-force relationship in an overspeed condition, while generating a sharply increasing force for triggering the overspeed emergency brake; where the overspeed detector magnet is translated with respect to the kinematic constraint element or the overspeed detector magnet is moved across the reaction surface due to the kinematic constraint element whereby the surface of the overspeed detector magnet is completely overlapped with the reaction surface, or where the kinematic constraint element is started to resonate at an amplitude which triggers the overspeed emergency brake by modulating the brake actuation force by a periodic feature. where the overspeed detector magnet is translated with respect to the kinematic constraint element or the overspeed detector magnet is moved across the reaction surface due to the kinematic constraint element whereby the surface of the overspeed detector magnet is completely overlapped with the reaction surface, or where the kinematic constraint element is started to resonate at an amplitude which triggers the overspeed emergency brake by modulating the brake actuation force by a periodic feature.