A method and sensing apparatus for elevators that detects an intrusion into a volume defined relative to a path across an opening. The sensing apparatus has a closure member for the opening that can be controllably displaced to define a gap in the opening. A first group of at least two emitters of electromagnetic signals located on either the closure member or a boundary member are directed into the volume and a second group of at least two receivers for electromagnetic signals located on the opposite side of the gap to the emitters. The method causes at least one of the emitters to emit a primary beam along a first axis into the volume, allows at least one of the receivers to receive a secondary beam of radiation, and enables one or more of the receivers to provide an output signal into the network.