An optical sensor (1) to detect objects within a monitored region includes a housing (3) having a window. The sensor includes a transmitting/receiving unit (6) arranged inside the housing and rotatable around an axis. The transmitting/receiving unit (6)includes a transmitter (8) to emit light rays (7) and a receiver (10) to receive light rays (9). The transmitted light rays (7) and the received light rays (9) are conducted through the window (12) in the housing. The window is optically adapted to shape the transmitted light rays (7) and the received light rays (9) into beams.