The invention relates to a device and a method for identifying an object O in an opening that can be closed by means of a mobile element (12). Light is fed into at least one fiber-optic light guide (33, 34) from a light source (1, 2), and variations in the received light are detected by means of at least one receiver (Ea, Eb), the fiber-optic light guide being arranged at least partially along the edge of the opening (11). A first fiber-optic light guide sends light transversally to the length thereof, said light being then received by a second fiber-optic light guide transversally to the length thereof. The second fiber-optic light guide (34) is connected to the receiver (Eb). The fiber-optic light guides are arranged on the edge of the opening (11) in such a way that a light field (F) at least partially bridging the opening is produced. At least one light source (1, 2) and at least one receiver (Ea, Eb) are respectively associated with each fiber-optic light guide (33, 34), and a clock circuit is used to alternately feed the light received by the respective receiver into the fiber-optic light guides. Comparison means are used to compare the signals on the receivers in order to identify the object.