Optical sensor according to the time-of-flight principle for detecting objects in a monitored region, having a first transmitter for transmitting first light pulses (22; 41) into the monitored region, a first receiver for detecting first light pulses (23; 51) radiated back by a first object to be detected in the monitored region, a second transmitter for transmitting second light pulses (32; 61) into the monitored region, a second receiver for detecting second light pulses (33; 71) radiated back by the first object or a further object in the monitored region, at least one control and evaluation unit (26, 36), which is designed to control the first transmitter and to evaluate the first light pulses (23; 51) detected by the first receiver and to control the second transmitter and to evaluate the second light pulses (33; 71) detected by the second receiver, wherein between the first transmitter and the second receiver, in particular internally, a first optical reference path is formed, wherein between the second transmitter and the first receiver, in particular internally, a second optical reference path is formed, wherein the at least one control and evaluation unit (26, 36) is designed • to trigger the first transmitter to transmit first test light pulses which reach the second receiver on the first optical reference path, and to activate the second receiver after a first time offset, the first time offset corresponding to a time of flight of the first test light pulses over the first optical reference path and / or • to trigger the second transmitter to transmit second test light pulses which reach the first receiver on the second optical reference path, and to activate the first receiver after a second time offset, the second time offset corresponding to a time of flight of the second test light pulses over the second optical reference path, and • to evaluate the first test light pulses detected by the second receiver and / or to evaluate the second test light pulses detected by the first receiver. a first transmitter for transmitting first light pulses (22; 41) into the monitored region, a first receiver for detecting first light pulses (23; 51) radiated back by a first object to be detected in the monitored region, a second transmitter for transmitting second light pulses (32; 61) into the monitored region, a second receiver for detecting second light pulses (33; 71) radiated back by the first object or a further object in the monitored region, at least one control and evaluation unit (26, 36), which is designed to control the first transmitter and to evaluate the first light pulses (23; 51) detected by the first receiver and to control the second transmitter and to evaluate the second light pulses (33; 71) detected by the second receiver, wherein between the first transmitter and the second receiver, in particular internally, a first optical reference path is formed, wherein between the second transmitter and the first receiver, in particular internally, a second optical reference path is formed, wherein the at least one control and evaluation unit (26, 36) is designed • to trigger the first transmitter to transmit first test light pulses which reach the second receiver on the first optical reference path, and to activate the second receiver after a first time offset, the first time offset corresponding to a time of flight of the first test light pulses over the first optical reference path and / or • to trigger the second transmitter to transmit second test light pulses which reach the first receiver on the second optical reference path, and to activate the first receiver after a second time offset, the second time offset corresponding to a time of flight of the second test light pulses over the second optical reference path, and • to evaluate the first test light pulses detected by the second receiver and / or to evaluate the second test light pulses detected by the first receiver. • to trigger the first transmitter to transmit first test light pulses which reach the second receiver on the first optical reference path, and to activate the second receiver after a first time offset, the first time offset corresponding to a time of flight of the first test light pulses over the first optical reference path and / or • to trigger the second transmitter to transmit second test light pulses which reach the first receiver on the second optical reference path, and to activate the first receiver after a second time offset, the second time offset corresponding to a time of flight of the second test light pulses over the second optical reference path, and • to evaluate the first test light pulses detected by the second receiver and / or to evaluate the second test light pulses detected by the first receiver.