Siren Coverage Calculator
A siren only alerts where it clears the background noise. Enter the siren’s rated output at 1 m, the ambient noise, the margin it needs to actually alert, and the area to cover — and get the free-field audible radius, the area one siren covers, and how many sirens you need. Planning figures; runs in your browser.
The audible radius is where the siren still clears ambient noise by your margin, using the inverse-square law SPL = dB − 20·log₁₀(r). It assumes open free field — real rooms and outdoor obstacles reduce it.
- Threshold to be heard (ambient + margin)60 dB
- Audible radius (free field)316.2 m
- Coverage per siren (π × r²)3,14,159 m²
- Area ÷ coverage (rounded up)1 siren
Planning estimate only — this is an open free-field figure. Walls, doors, furniture and outdoor obstacles all cut real coverage sharply, and datasheet dB ratings are measured in ideal conditions. Pair an outdoor siren (deters and alerts neighbours) with an indoor sounder (wakes occupants); a self-powered outdoor sounder keeps sounding if the cable is cut, and a strobe helps in noisy or hard-of-hearing settings. Use this to compare options, then confirm with a real site sound test.
Plan the alarm, not just the siren
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False-Alarm Risk