There is disclosed a method of testing an optical door sensor 100 having an emitter 102 for emitting a light signal 104 and a receiver 106 for detecting the light signal 104, the optical door sensor 100 having at least one sensor operating parameter and further having a baseline state in which the receiver 102 can detect a light signal from the emitter 106. The method comprises setting the optical door sensor in an offset state 204, 304, in which a sensor operating parameter is offset from a baseline setting by an offset amount, the baseline setting corresponding to the baseline state of the optical door sensor; conducting a signal test 206 with the optical door sensor in the offset state; and generating an alert 216 when the signal test result is negative for the offset state and the offset amount is less than or equal to a limit margin. The signal test comprises: emitting a light signal from the emitter 208 and determining whether the light signal is detected by the receiver 210. The signal test has a positive result if the light signal is detected by the receiver and a negative result if the light signal is not detected by the receiver.