The five CO detectors that PS tested included, from left, the CO Star, the Fireboy/Xintex CO Sentinels (these small rectangular units are identical except that the more expensive one on the right will interface with other units installed on a vessel), the Safe-T-Alert (bottom middle), and the Fireboy/Xintex 9V.

Consider this not-so-unusual scenario: On June 18 this year, a group of friends rafted up three midsize vessels at an idyllic anchorage on Silver Glen Springs in northern Florida. They were intent on spending the night at this placid, popular spot near the Ocala National Forest.

At 5:00 p.m., the generators on all three boats were turned on to power air conditioners for a comfortable night's sleep belowdecks. Those to port and starboard of the center vessel operated portable generators placed on their swim platforms. The center vessel operated an onboard generator discharging exhaust via a port on the starboard quarter, just above the waterline. A rectangular foam fender was…