The Pro-Lab® professional carbon monoxide test kit and detector is a stick-on carbon monoxide detector that detects invisible and odorless gas. Testing is safe and easy. Simply place the detector onto a wall, a door or other surface and wait for it to turn in color, if the spot turns gray or black- CO is present. Once the CO is gone and the air is clean, the spot returns to its original color. Kit includes two reusable sensor buttons. More sensitive than electronic detectors and provides accurate and reliable results. Ideal for use in boats, airplanes, RV's, cars, homes and much more! This test has been laboratory tested for accuracy.