Carbon Monoxide Chemical detectors - How It Works

These simple detectors are pieces of cardboard with a small orange-colored circle in the middle. If there is a high-level of carbon monoxide in the vicinity, the circle changes color from orange to black. This happens as a direct result of chemistry. The detector circle is gritty and sand-like; it is silica gel impregnated with a catalyst made from chemicals that include palladium and molybdenum salts (such as palladium sulfate and ammonium molybdenate).

When carbon monoxide touches the detector, it's oxidized by the chemical salts on the strip and turns into carbon dioxide. The chemicals on the strip are simultaneously reduced and change color to black. The strip also contains a chemical salt made from a transition metal such as iron, nickel or copper. Once the carbon monoxide is removed, this metal salt steals some oxygen from the air and changes the catalyst back to its original chemical form—so the detector spot changes color back to orange again. In other words, the catalyst regenerates itself in the air.

The advantage of simple detectors like this is that they cost only a few dollars each, so they're a good way to give yourself basic protection. The disadvantage is that these detectors don't sound an alarm: you have to keep looking at them to notice that the color has changed. These strip detectors have to be replaced every 3-6 months depending on the environment you’re using them in; an expiration date is on every package.