Alarms and Detectors Light Meanings

Browse smoke alarm and carbon monoxide detector lights, including red, green, yellow, low battery, alarm memory, and end-of-life indicators.

Alarms and Detectors guides

RedBlinkingSafety

Smoke Alarm Blinking Red Light

A blinking red light on a smoke alarm can mean normal operation, a recent alarm event, low battery, hush mode, or a device-specific warning depending on the model.

Smoke Alarm Lights · General

RedSolid or flashingEmergency Possible

Carbon Monoxide Detector Red Light

A red light on a carbon monoxide detector can indicate alarm, fault, memory, low battery, or end-of-life depending on the model. Treat any CO alarm as serious.

Carbon Monoxide Detector Lights · General

RedBlinkingSafety

First Alert Blinking Red Light

A blinking red light on a First Alert alarm can mean normal operation, alarm memory, an active alarm, low battery, or another model-specific condition.

Smoke Alarm Lights · First Alert

GreenSolid or blinkingNormal or Check Soon

First Alert Green Light

A green light on a First Alert alarm often indicates power or normal operation, but the exact meaning depends on the model and whether the light is steady or blinking.

Smoke Alarm Lights · First Alert

RedSolid or blinkingSafety

Kidde Smoke Alarm Red Light

A red light on a Kidde smoke alarm can indicate normal status, alarm memory, active alarm, low battery, hush mode, or a model-specific warning.

Smoke Alarm Lights · Kidde

Yellow, amber, red, or display indicatorModel-specificSafety

CO Detector End-of-Life Light

A CO detector end-of-life light means the alarm has reached the end of its sensor life and should be replaced, not ignored.

Carbon Monoxide Detector Lights · General

YellowSolid or blinkingSafety

Smoke Alarm Yellow Light

A yellow light on a smoke alarm usually means attention is needed, such as low battery, fault, hush mode, end-of-life, or a model-specific maintenance condition.

Smoke Alarm Lights · General

GreenSolidNormal

Smoke Alarm Solid Green Light

A solid green light on a smoke alarm usually means the alarm has power or is operating normally, but the exact meaning depends on the model.

Smoke Alarm Lights · General

GreenSolid or blinkingNormal

CO Detector Green Light

A green light on a carbon monoxide detector usually means the alarm has power or is operating normally, depending on the model.

Carbon Monoxide Detector Lights · General

How to troubleshoot alarms and detectors lights

Start with the exact device type, then narrow the signal by color and pattern. A solid light can mean something very different from a blinking, flashing, pulsing, or alternating light. If the device has a screen, mobile app, error code, alarm sound, or label beside the light, use that information too.

For safety-sensitive devices, do not rely on color alone. Smoke alarms, carbon monoxide detectors, vehicle warnings, batteries, chargers, medical equipment, and electrical devices should always be checked against official guidance.

Good first checks

Check power and cables before changing settings.
Write down the exact color and blink pattern.
Check the app, display, or error message if one exists.
Look for the exact model number.
Avoid factory resets until simpler checks fail.