The First Alert CO400 is a basic battery-powered carbon monoxide alarm with an electrochemical sensor, a replaceable 9-volt battery, an 85 dB horn at 10 feet and an end-of-life warning. It detects CO only. It doesn’t detect smoke or natural gas. It’s a good fit for adding CO coverage where there’s no outlet or hardwired circuit, in a home that already has working smoke alarms.
This page uses First Alert’s product page and manual. Nobody tested the alarm for it.
Published features
| Feature | First Alert CO400 |
|---|---|
| Sensor | Electrochemical CO sensor |
| Power | One replaceable 9V battery; no hardwire or plug-in option |
| Alarm | 85 dB at 10 feet |
| Warnings | Low-battery signal and end-of-life warning |
| Controls | One test/silence button |
| Warranty | Seven-year limited |
First Alert doesn’t list interconnection for the CO400, so expect it to sound only where it’s mounted. If your local code calls for hardwired, interconnected or combination alarms, or you want one alarm to trigger every unit in the house, choose a model built for that instead. First Alert sells many alarms with similar names, so confirm “CO400” on the package.
Where to put it
The U.S. Fire Administration recommends CO alarms in a central spot outside each sleeping area and on every level of the home, mounted as the manufacturer’s instructions direct. Follow the CO400 manual and local code for exact placement.
Ownership
Press the test button on the schedule in the manual. Learn which sound means alarm, low battery, malfunction and end of life. A unit with a dead or missing battery gives no protection, so replace the 9V when it signals. When the end-of-life warning starts, replace the whole alarm, even if it still looks new. Write the install date on the alarm.
If it goes off, get everyone into fresh air and call 911 or your fire department as the manual directs. Headache, dizziness, nausea or confusion can mean CO exposure. Don’t go back inside just because you opened windows. Never run a generator, grill or vehicle inside the house or in an attached garage.
Verdict
The CO400 is a sensible way to add CO detection to a room or level that lacks it. It isn’t a complete alarm plan. Keep code-compliant smoke alarms, and choose a plug-in, hardwired or interconnected model where code or your layout calls for one.