Active infrared detectors are extremely flexible and versatile and can be used for the protection of secondary closing edges or even for the activation of doors in confined spaces. Integrated active infrared detector configurations can be used to configure the detection of a wide variety of safety areas for standard and curved sliding doors. Two active infrared detectors extend the field so that any contact of persons with the door can be avoided. Doors on sidewalks and passages can be controlled via an active infrared detector so that people passing by do not open the door unintentionally. On standard doors, active infrared detectors monitor the secondary closing edge without a protective leaf.