Sensitivity and radio range get specified in every PIR enquiry. The lens shape rarely does, and it is the single choice that most often makes a correctly built sensor behave like the wrong product. A dome lens and a curtain lens are the same pyroelectric element behind different optics — which means the same SKU can cover a room or guard a boundary, and the specification that decides between them costs nothing to change before tooling and a support ticket after it.
What the optics actually project
A dome (wide-angle) lens projects a fan of segments across roughly 90 to 110 degrees, at detection depths of up to 12 metres. It is the right answer wherever the requirement is "anything moving in this volume": living rooms, offices, retail floors. Its weakness is directional: an intruder moving straight at the sensor crosses fewer segment boundaries than one moving across the pattern, and slow, head-on approach is the classic miss.
A curtain lens collapses that fan into a narrow, deep strip — typically a metre or two wide and 10 metres or more long. It exists to protect a line rather than a volume: the strip in front of a window, the face of a glass wall, a boundary along a corridor. Movement across the boundary — the direction an intruder actually moves — cuts perpendicular through every segment, which is exactly the geometry PIR detects best. The same directional weakness that hurts domes becomes a strength: passers-by outside the strip never trigger it.
Choosing by route, not by room
The question that picks the lens is not "how big is the space" but "where does the moving person travel". A long corridor is a curtain problem even though it is a room: a dome pointed down a corridor wastes its fan on the walls and sees the approach head-on, the worst-case geometry. A perimeter of floor-to-ceiling glazing is a curtain problem regardless of room width, because the requirement is a line at the glass, not coverage of the furniture. A warehouse aisle with racking that blocks half a fan is a curtain problem, too.
Rooms where movement happens anywhere — and where the budget wants one sensor per space — stay dome territory. Mixed deployments are normal: domes for the interior, curtains at the glazing line, and that split is cheaper than over-tilting domes at windows or over-sensitising a corridor unit until drafts trigger it.
Masking, altitude of the cone, and the pet interaction
Lens choice interacts with the other specification lines. A dome aimed at a window usually needs segment masking to ignore the glass and what moves behind it; a curtain aimed at the same window may need none, because the street beyond sits outside its strip — or entirely inside it, depending on aim, which is why the strip's end-stop distance is a spec, not a surprise. Pet immunity complicates the picture further: a pet-immune dome ignores floor-level movement by ignoring the lowest segments, while a curtain at the glass line intersects pet territory at a fixed plane and needs its strip to start above the animal's stated weight class, not just its shoulder height.
These interactions are why lens shape belongs in the project conversation instead of the accessory list. Swapping it later means new tooling or a new SKU, not a firmware update.
What to specify, in buyer terms
Three lines settle it. First, the route map: where people and intruders move, drawn on the plan. Second, the lens per zone — dome for volumes, curtain for lines — with the strip dimensions and end-stop distance stated for the curtain zones. Third, the masking and pet-immunity interaction per zone, so the immune model's weight claim survives the mounting geometry.
XingLiao manufactures PIR motion sensors with dome, curtain and long-range optics as variants of shared platforms, specified per project as OEM/ODM programmes. Buyers can send the route plan and receive the lens-per-zone proposal with the quotation.
The short version
The lens is the coverage: a dome watches a volume and fears head-on approaches; a curtain watches a line and thrives on them. Choose by where movement travels, state strip dimensions and masking per zone, and settle it before tooling — after tooling it is a SKU change, not a setting.
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