Smoke Alarm or Smoke Detector?

by Harry J. Oster

Would you call a pike ax a flathead ax, or a smooth bore nozzle a fog nozzle? I don't think so.

So why then would you call a single station smoke alarm (photo 1) a smoke detector? Why would you call a smoke detector a smoke alarm? I'm not sure why either, but let's look at the difference.

Although they look alike, a smoke alarm is a stand-alone device with a built-in audible sounder, a control component such as a power supply (typically battery or electric with battery backup), and a sensor. A smoke alarm is not connected to a fire alarm control panel, but it may sound several smoke alarms within the building if it is interconnected with other smoke alarms,

On the other hand, a smoke detector (photo 3) typically has only a built-in sensor and is part of a system. This means that to function, the detector also requires an external sounding audible device (such as a horn/strobe unit) and a control component such as a power source, typically found at the fire alarm panel.

Also, note that the fire alarm panel may or may not send a signal (typically to a central station) for an automatic fire department response. If the panel causes only the audible sounder inside the building to sound, anyone hearing the audible alarm would then need to manually call 911 for a fire department response.


(1) A typical single station smoke alarm. Note the test button on the lower right.
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(2) A typical single station smoke alarm. Note the power supply, sensor, and sounder.
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(3) A typical smoke detector that is part of a system. The unit only has a sensor--no built in power supply or sounder. Many smoke detectors can be removed from a secured ceiling-mounted base and replaced when necessary.
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What defines the two types?

National Fire Protection Association(NFPA) 72, National Fire Alarm Code, defines a smoke alarm as a single- or a multiple-station alarm that is responsive to smoke. This is followed by the definition of a single station, which is a detector comprised of an assembly that incorporates a sensor, control components, and an alarm notification appliance in one unit or obtained at the point of installation.

A smoke detector is defined under "detector" as a device suitable for connection to a circuit that has a sensor which responds to physical stimulus such as heat or smoke. It is further defined under "smoke detector" as a device that detects visible or invisible particles of combustion, therefore lacking the control components and an alarm notification appliance found as part of a smoke alarm.

Note: Some system-powered smoke detectors found in hotels, apartments, dorms, and lodging houses may have attached sounder bases that sound locally as a smoke alarm does, but they are actually detectors that are part of a system with a fire panel.

Why should you know the difference?

Have you ever tried looking for or instructing your inside investigation team to locate the fire panel to silence a smoke alarm? What about, after locating an activated smoke alarm, asking the homeowner, "Where is your fire panel located?" This could be a real embarrassment for your department.

A more embarrassing moment might be if the type of device (smoke alarm or smoke detector) is not correctly stated in your report and you are called to testify and read your report in court. If not stated accurately, on cross examination the defense attorney may use this inaccuracy to his advantage.

Are there similarities between the two?

Yes. For both types, the typical installation locations and spacing guidelines (900 square feet and maximum 30 feet on center) are the same. The sound emitted from a smoke alarm or an audible device as part of a fire alarm system using detectors, since July 1, 1996, is required to be the same American National Standard ANSI S3.41 Audible Emergency Evacuation Signal and International Standard ISO 8201 Audible Emergency Evacuation Signal Temporal 3 sound (beep, beep, beep, stop, and so forth), and both require a degree of inspecting, testing, and maintenance in accordance with NFPA 72.

This information will be important if you are investigating or writing a report for an activated smoke alarm or smoke detector.

Harry J. Oster is a 20-year veteran of the fire service. He holds an associate's degree in fire protection technology; is a certified New York State code enforcement official; code compliance technician and fire investigator II; IAAI fire investigator (CFI); NFPA fire protection specialist (CFPS) and fire inspector I; ICC fire inspector II; NPQS (Pro-Board) fire inspector I and NICET fire alarms II.

The information and views expressed in this article are meant for informational purposes only and are based on research performed by the author. The material does not necessarily reflect the views of other members of the fire service. Obtain legal advice before attempting to act on any of the above information or applying to any field application. The author does not recommend or endorse any manufacturer. Photos shown are for illustration proposes only.

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