Electrochemical detectors are battery-powered and have a few more bells and whistles than the others, including a continuous digital readout an LCD display, and a memory feature that allows you to check CO levels that occurred in your absence. But one compromise may be selectivity-that is, how well the detector can sense CO that's mixed with other gases. In the Lawrence Berkeley test for selectivity, the electrochemical detectors failed 10 percent of the time. In fairness, most of the failures came from a Coleman product that has since been pulled from the market, and McMahan says that concentrations of common household gases used in that test were well above typical levels. No matter which detector you choose, it's important to know where to install and how to maintain it.
Manufacturers recommend that every occupied floor of a house have a detector.
But if you opt for only one alarm, install it in the hallway outside the sleeping area. Don't take chances. If any member of your family is experiencing flu-like symptoms, also check for carbon monoxide. If it's a plug-in model, don't use an outlet controlled by a wall switch. Keep detectors at least 10 feet distant from a fuel-burning appliance and away from most household chemicals or aerosols.