The invention relates to the monitoring of a brake (400, 500). The brake (400, 500) comprises first and second braking surfaces (204, 206) and magnetizing means (210) arranged to move the braking surfaces (204, 206) to an open state, in which the braking surfaces (204, 206) are separated from each other, and to a closed state, in which the braking surfaces (204, 206) are connected to each other. During the monitoring of the brake (400, 500), the time is measured that elapses from the change in the magnetic field caused by the magnetizing means (210) to the shift of the braking surfaces (204, 206) from one state to another.