Professional carbon monoxide test kit & detector detects invisible & odorless Gas stick on carbon monoxide detector safe & easy to use more sensitive than electronic detectors & provides accurate & reliable results replace sensor button every 6 x months un-opened sensor buttons shelf life is 3 years great for use in boats airplanes RV s & automobiles includes: detector & 2 reusable sensor buttons laboratory tested for accuracy. This test kit detects the invisible and odorless gas it is more sensitive than electronic detectors. If carbon monoxide is present the sensor button will return to its original color and be ready for reuse when exposed to fresh air. Even a slight darkening of the sensor button indicates a dangerous amount of carbon monoxide.