A movement and/or a position of an object (1) to be monitored is detected. At least one marker (2) radiating light is arranged in an area of the object (1) such that a camera (4) can capture images of the marker (2), when the object (1) is in a first position. An image processing unit (6) is enabled to detect the marker (2) in the images and to detect a movement and/or a second position of the object (1) in response to determining that at least a part of the marker (2) cannot be detected in one or more of the images. The object (1) may be a person laying in a bed and the marker (2) may be arranged adjacent to the bed's lying area (3) so that the system can detect when the person leaves the bed and notify nursery staff or an emergency central.