An optical communication probe enables a diagnostic tool to optically communicate with an external device, such as an appliance, through a low intensity indicator light of the external device. The communication probe includes an optical transmitter, an optical receiver, and a housing in which the optical transmitter and optical receiver are mounted. The optical transmitter transmits light signals having a logical polarity that is the opposite of an indicator light associated with an indicator light of an external device with which the optical transmitter is communicating. Use of the opposite logical polarity improves the noise immunity for the optical communication between the communication probe and the external device.