Guardian Avionics AERO 553-101-001 Multi-Function Carbon Monoxide (CO) detector is a panel mounted TSO Certified unit designed especially for use in both FAA certified aircraft and experimental aircraft. This unit was designed to fit in, and replace a standard 2.25-inch instrument panel clock. AERO 553 features a clock, timer, temperature, cabin, and density altitude functions along with highly accurate and extremely fast CO detection and PPM readings within the cockpit on an easy-to-read LCD display.