the radiation that can be measured by the sensor subsystem obviously this application requires a light to be the external device to connect to hence in particular for this application the system in particular the sensor subsystem 12 could be integrated with the light unit in a single device for instance within a luminaire or lamp preferably with a light bulb or a unit that can be put in a standardized light bulb screw base in summary the present invention provides a system and a method for reliably monitoring the presence of a person in a monitored area the proposed system and method can also be applied when the person is covered by clothes or a blanket or when the monitored area is lying in the dark compared to other known systems the number of false alarms can be kept low in particular after an appropriate calibration of the system still further no additional hardware needs to be attached to the elements e g a bed within the monitored area so that the system can be generally used for various applications and in various situations e g can be simply moved from a first monitored area to another monitored area or simply another bed with another person can be moved into the monitored area as will be often the case in a hospital the invention has been illustrated and described in detail in the drawings and foregoing description but such illustration and description are to be considered illustrative or exemplary and not restrictive the invention is not limited to the disclosed embodiments other variations to the disclosed embodiments can be understood.