Fireboy-Xintex CMD6-MD-R CO Alarm 12/24V DC with Relay - White

The Fireboy-Xintex CMD6-MD-R is the premium marine carbon monoxide alarm for boats and RVs - 12V / 24V DC operation with backup batteries, plus the 'R' variant's internal relay and Interconnect capabilities that step it up from a standalone alarm to an integrated safety system. For boat owners building serious marine safety systems and meeting current ABYC and Coast Guard safety standards, the CMD6-MD-R is the right call.

Why marine CO alarms matter - the silent killer at sea. Carbon monoxide is colorless, odorless, tasteless, and lethal at concentrations of 400-1600 ppm (parts per million) over hours of exposure. Marine sources include: gasoline and diesel engines (especially during idle or low-RPM operation where combustion is incomplete), gas generators, gas heaters (LP propane heaters used in cabin heating), gas stoves and ovens, and exhaust from nearby boats in marina and dock situations. The 'station wagon effect' on boats with cabin areas behind the engine compartment can pull engine exhaust into accommodation spaces under certain wind / current conditions - even with no obvious source of CO. The U.S. Coast Guard has documented multiple recreational boating fatalities each year from CO exposure on properly-operating boats. CO alarms are required equipment for boats with enclosed cabins where occupants sleep or spend extended time.

What 'CMD6' means - the latest generation. The CMD6 is Fireboy-Xintex's current-generation marine CO alarm series, the successor to the CMD5 series. Key improvements over CMD5: improved sensor accuracy and longevity, refined microprocessor control with better TWA calculation, lower standby power draw (4 mA - down from higher draw on older units), and the 'R' variant's internal relay / Interconnect functionality. CMD6 uses the same housings, mounting brackets, and wire connections as CMD5, so existing CMD5 installations can upgrade to CMD6 without re-wiring or re-mounting - drop the new alarm into the old mounting plate, reconnect the existing wires, and you've got an upgraded system. Drop-in compatibility matters for boats where the original install was in a hard-to-reach location.

What 'MD' means - 12/24V DC powered with backup. The MD variant runs on the boat's 12V or 24V DC power supply - same circuits powering the rest of your boat's electronics. Permanent internal lithium-metal backup batteries take over if the boat power goes out (low battery state, breaker tripped, wiring failure), keeping the alarm operational during the conditions where you'd most need CO protection. The MD variant is the install-once standard - wire it to the boat's accessory bus and forget about it, no battery changes ever (the backup batteries are permanent for the unit's service life). The alternative CMD6-MB variant runs 100 percent on permanent internal batteries with no external power needed - simpler install but less integrated with the boat's electrical system.

What 'R' means - internal relay AND Interconnect. The 'R' suffix is what makes this the premium variant. (1) Internal relay: dry contact output that activates when the CO alarm triggers - the relay can drive external loads like: secondary alarm horns mounted at the helm or in remote spaces (so the alarm is heard outside the immediate cabin), engine kill systems (automatically shut down generators or auxiliary engines that may be the CO source), fume blowers or extraction fans (automatically ventilate the affected space), or integration with the boat's monitoring system. (2) Interconnect functionality: multiple CMD6-MD-R alarms can be wired together so when ANY alarm triggers, ALL alarms in the system sound. Critical for boats with multiple accommodation spaces (forward cabin, main salon, aft cabin, captain's quarters) - without Interconnect, an alarm sounding in the forward cabin might not wake someone in the aft cabin. With Interconnect, all alarms sound simultaneously, ensuring everyone aboard is alerted regardless of their location.

Time-Weighted Average measurement - what it does. Simple CO alarms trigger at a fixed CO concentration threshold (typically 70 ppm). The CMD6 uses Time-Weighted Average (TWA) measurement that's more sophisticated: continuously monitors CO concentration, temperature, and exposure time to calculate Carboxyhemoglobin (COHb) - the blood saturation level of CO bound to hemoglobin. The alarm triggers at 10 percent COHb - the medically established threshold for serious CO health effects (impaired judgment, dizziness, headache). The TWA approach prevents false alarms from brief CO spikes (cooking with the stove, briefly idling next to an exhaust source) while catching the dangerous long-duration low-level exposure that kills people on boats overnight. The medical-grade COHb measurement is the right approach for life-safety equipment.

10 percent COHb alarm point - what it means. 10 percent COHb is the established medical threshold for serious CO health effects. At lower COHb levels (below 5 percent), most people experience no symptoms. At 10 percent, symptoms become noticeable (headache, mild dizziness, reduced motor coordination). At 25 percent, severe symptoms begin (vomiting, loss of consciousness). At 50+ percent, death typically occurs. The 10 percent alarm point gives meaningful early warning before serious health impact - well before the dangerous higher COHb levels. The TWA calculation means a sustained low-level CO exposure that accumulates to 10 percent COHb triggers the alarm even if the instantaneous CO concentration is below typical fixed-threshold alarms.

85 dBA alarm horn. The audible alarm is rated 85 dBA at 10 feet - loud enough to wake sleeping occupants and audible throughout typical boat accommodation spaces. The frequency is tuned to penetrate cabin walls and reach occupants in adjacent spaces. For boats with multiple accommodation spaces, combine multiple CMD6-MD-R alarms with Interconnect functionality so all alarms sound simultaneously - the combined volume in any one space is loud enough to wake even heavy sleepers.

4 mA standby power draw. The CMD6-MD-R draws just 4 milliamps during normal standby operation - effectively negligible on the boat's electrical system. For comparison, a typical LED cabin light draws 500 mA. 4 mA is small enough that the alarm can run continuously 24/7 without measurable battery drain over weeks of unattended boat storage. The low draw also means the backup batteries (when in use after primary power loss) can power the alarm for extended periods - days to weeks depending on how often the alarm triggers.

7-year sensor end-of-life. The CO sensor element has a finite useful life - typically 7 years from initial installation. The CMD6 monitors sensor health and signals end-of-life with a distinctive periodic chirp when the sensor needs replacement. When you hear the end-of-life signal, replace the entire alarm - sensor replacement isn't field-serviceable on consumer-grade CO alarms. Plan for replacement at the 7-year mark to ensure continuous CO protection.

Chemical resistance. The CMD6 housing and sensor are designed to resist common marine chemicals: cleaning solvents (acetone, mineral spirits, isopropyl alcohol), marine cleaners, polishing compounds, varnish vapors, and other typical boat-environment chemicals. Older CO alarms could be desensitized or damaged by exposure to these chemicals - the CMD6's chemical resistance is meaningful for the marine environment where these substances are common.

Install considerations. Mount in each accommodation space (cabin, salon, sleeping quarters) - boats with multiple separate cabins need one alarm per cabin. The CO alarm should be mounted at sleeping-occupant breathing height (typically 5-7 ft above the cabin sole, on a vertical bulkhead vs the ceiling). Avoid mounting: directly above the galley stove (false alarms from cooking), near opening hatches (false alarms from outside CO sources), in spaces where the temperature varies wildly (engine room, exposed outdoor locations), or behind furniture or curtains that block airflow. Wire to the boat's 12V or 24V DC accessory bus - dedicated circuit preferred but a shared circuit is acceptable given the 4 mA draw. For the 'R' variant relay and Interconnect features, run the relay and Interconnect wires per the included installation manual to your specific application.