Smoke detector
Marks where a smoke detector is installed. Drawings use more than one symbol for it, so the legend says which is meant.
Easily confused with
How to read it
NECA 100 lists a smoke detector among its fire alarm sensor symbols, with separate symbols for duct smoke detectors, beam detectors and self-contained single-station detectors. It notes that the fire protection industry publishes its own symbols, not all of them in wide use on electrical drawings. The Army Corps of Engineers' A/E/C CAD Standard gives smoke detectors as an example of the objects drawn on plans as symbols.
Also searched as: smoke alarm symbol.
This explains what a symbol represents on a drawing. Conventions vary between firms and standards, and a drawing's own legend takes precedence.
Look-alikes
In the Army's print-reading manual, SD is the symbol for a door switch. On an electrical plan the two can look alike, and the legend tells them apart.
Read next
- Next in Blueprint symbolsToiletA toilet, seen from above: the tank and the bowl. On plumbing drawings a toilet is a water closet.
- In Smoke and CO alarm soundsThree beeps and a pause (smoke alarm)A smoke or fire alarm sounding for smoke or fire. Three beeps and a pause, repeating, is the temporal-3 pattern, the standard emergency evacuation signal.
More blueprint symbols
The same shape elsewhere
Browse symbols drawn with circles or letters and numbers.
Sources
- Symbols for Electrical Construction Drawings, NECA 100-2013 (ANSI), National Electrical Contractors Association (Internet Archive copy), sec. 7.2, symbols 7.202 and 7.207; sec. 2.2
- Construction Print Reading in the Field, TM 5-704 / AFM 85-27, Departments of the Army and the Air Force, app. B, fig. B-9
- A/E/C CAD Standard, Release 4.0, ERDC/ITL TR-09-2, U.S. Army Engineer Research and Development Center, CAD/BIM Technology Center, ch. 4, symbols
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 24, 2026. How we research
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