Because outdoors everything moves and the temperature range is enormous - an indoor detector in a weatherproof housing produces continuous false alarms.

Vegetation in wind, rain, snow, animals and vehicles all generate the signals an indoor detector reports.

Direct sunlight and rapid temperature change defeat the contrast an infrared sensor depends on.

Outdoor detectors use two technologies in AND, digital pattern analysis and temperature compensation specifically to handle this.

They are also built for the environment: sealed, ultraviolet-stable, and rated across a wide temperature range.

The processing is the difference, not the housing - which is why a weatherproof enclosure around an indoor sensor is not a solution.

Curtain where the protection is a line - a facade, a boundary, a row of windows - because it excludes everything beyond the plane.

A curtain pattern is a narrow vertical plane. Someone crossing it is detected; anyone beyond it is not.

That is exactly what is wanted along a boundary next to a public footpath, where a volumetric detector would report every passer-by.

Volumetric patterns cover an area such as a yard, a car park or a courtyard, and are far more exposed to environmental triggers.

Curtain detection also gives a cleaner alarm: the line was crossed, at this point, at this time.

Where an area genuinely must be covered, expect to pair it with camera verification rather than acting on the detector alone.

It detects an attempt to cover or obstruct the sensor, which matters because an outdoor detector can be reached before the intrusion happens.

An intruder who sprays, tapes or hangs something over a detector disables it silently, then returns later.

Anti-masking uses an active sensing element to detect an object placed close to the lens and reports it as a fault or a tamper.

It also catches accidental obstruction - a growing shrub, a stored pallet, a spider's web - which is a genuine maintenance benefit.

The alarm has to go somewhere that produces a response, or it is a feature that achieves nothing.

Higher alarm grades commonly require anti-masking on external detection, so check the local grading scheme.

By pairing detection with verification - a camera on the same zone, an operator look, or audio challenge - rather than dispatching on the detector alone.

Outdoor detection generates more activations than indoor detection, and always will.

Verification turns that from a problem into useful information: the detector says where to look, and a person or an analytic decides whether it matters.

Many response and policing arrangements require confirmation before attending, and the rules differ by jurisdiction, so check what the local scheme demands.

Two detectors in sequence, or a detector plus a beam, is another confirmation method.

Log and review activations. A single zone producing most of them usually has a physical cause that can be removed.

Lens cleaning, vegetation control and a check that the mounting is still rigid - all scheduled, not reactive.

Lenses accumulate dust, salt, cobwebs and insect debris, which reduces detection silently.

Vegetation grows into coverage over a season. A clear zone has to be maintained by whoever cuts the grounds, not by the alarm contractor on an annual visit.

Mountings loosen. A detector that has shifted covers somewhere other than where it was commissioned.

Seals and cable entries degrade under ultraviolet light and thermal cycling, and water ingress is the usual end of an outdoor detector's life.

Walk-test each zone on a schedule and record it. An outdoor detector that has stopped detecting looks exactly like one that is quiet because nothing has happened.