A method and apparatus for detecting objects has a sensor with a light source, a light receiver, and a light retroreflector between them. Light from the source is transmitted to the detector along a light transmission path from the source to the retroreflector and is reflected back to the detector along a light reflection path that substantially corresponds to the transmission path. A single lens or a pair of adjacent lenses shapes the respective light beams from both light emitted by the source and light reflected by the retroreflector in accordance with either the auto collimation principle or the double-eye principle, respectively. A polarizer and a beam splitter are arranged in the light transmission path for light from the source, and a polarization filter is arranged in the light reflection path so that light reflected by the retroreflector passes through the beam splitter and the polarization filter before it reaches the light receiver. A control unit recognizes an interruption of at least one of the light beams as the detection of an object in the light transmission and/or light reflection paths. The beam splitter is a dielectricum which has differing transmission and reflection characteristics for p-polarized light and s-polarized light.