spatial angle which is formed by component spatial angles 8 which are in turn sensed by the receiver of the sensor 10 if light which is emitted from the transmitter of the sensor reaches the marking unit 12 it is diffusely scattered and the marking unit 12 is sensed the corresponding angular region which can then be assigned to the movement element 13 is blanked out by the evaluation unit which is integrated in the monitoring unit 10 fig6 shows the corner between two walls 2 and 7 and also a monitoring sensor 20 which monitors component spatial regions 8 however the monitoring apparatus 20 is not only a safety apparatus but also an opening sensor which monitors a second monitoring region which is further away this is illustrated by a receiver which is oriented toward a region which is further away over the component spatial region 21 therefore both a safety monitoring operation and an opening monitoring operation can be performed by a single monitoring apparatus fig7 comprises a monitoring apparatus 30 which is fitted to a door frame and which again monitors a region by means of a safety apparatus in the horizontal direction over the component spatial regions 8 however an angle encoder 31 which is in the form of an optical angle encoder is additionally integrated the angle encoder comprises a light emitting diode which creates a spotlight which is incident on a marking unit 32 on the movement element this marking unit 32 on the movement element has a reflective surface and therefore the corresponding light beam is reflected back again and finally strikes a linear array sensor of the sensor 31 when the door 13 is pivoted the reflected beam moves along the line of the linear.