Two modes of testing Sensitest provides tests for all types of SpO2 probes in the biomedical and clinical environment. This compact devices draws power for two modes of testing from a single 9V Alkaline Battery. Mode 1 tests Continuity checks for the red LED, the infrared LED, and the photodiode circuits. Mode 1 Operation:Continuity checks for the red LED, the infrared LED, and the photodiode circuits. Mode 2 Operation:Measures and displays the photodiode’s response to red and infrared LEDs.