11.1 Passive Infrared Motion Detection

The New York Department of State (DOS) Security or Fire Alarm Installer written exam lists motion detection as its own topic. In the 81-hour qualifying course, that subject is the heart of Module 3, Security Systems. 19 NYCRR 196.8 Module 3, subject II, is MOTION DETECTION for 8 classroom hours — the largest security block in the outline, larger than the Module 3 time for perimeter, specialty, CCTV, or access control. Independent OpenExamPrep study material that helps candidates prepare for this exam treats those hours as security intrusion sensing, not as lighting occupancy control and not as fire-alarm smoke or heat detection. General Business Law (GBL) Article 6-D licenses security or fire alarm work. A candidate who studies only fire devices will miss the motion questions.

Why passive is an exam word

A passive infrared (PIR) motion detector is the common interior space-protection device on New York burglar-alarm jobs. Passive means the unit does not emit infrared energy. It receives long-wave infrared that objects already radiate because they are warm. A person, a pet, a space heater, and a sun-loaded floor all emit in that band. The PIR's job is to notice a change in received infrared as a target moves across its field of view. If a stem says the detector shoots an IR beam or pings the room with infrared, that stem is describing an active device, not a PIR.

The detector still needs power. Passive is not a synonym for unpowered. Hardwired PIRs draw from a zone, an auxiliary power output, or an addressable security bus. Wireless PIRs use a battery and still report to a listed control. Under 19 NYCRR 195.1(a), a security or fire alarm system is an aggregation of devices designed to signal intrusion, break-in, theft, movement, sound, fire, heat, smoke, explosion, and similar events. 195.1(c) names motion detectors among the devices whose placing and connection is installation. Wireless does not create a licensing loophole.

Pyroelectric sensing and temperature contrast

Behind the window is a pyroelectric sensor, usually a dual-element pair. Pyroelectric materials generate a small electrical signal when their temperature changes. A single element that simply warmed with the room would drift. Dual-element processing compares two portions of the field. When a warm or cold target crosses from one optical zone into the next, the two elements see a changing difference; the electronics treat that difference as motion. Slow, uniform changes — a room warming after the furnace starts — tend to affect both elements together and are rejected.

That physics requires temperature contrast. If an occupant's apparent temperature matches the background, or if a person walks straight at the unit along a single zone without crossing zone boundaries, the pair may not produce a usable signal. Exam items that mention a hot warehouse, no contrast, or walking directly toward the detector are testing this, not a Uniform Code height.

Fresnel lens: curtains versus volumetric coverage

Almost every listed security PIR uses a Fresnel lens — a thin, grooved plastic optic — instead of a heavy glass lens. The grooves divide the field of view into discrete detection zones. Crossing a zone boundary is what the electronics count. Lens design, not a marketing photo, sets the pattern:

A volumetric unit is a room trap. A curtain unit is a barrier across a path. Mixing them up produces both holes and false alarms. The installer reads the listing coverage drawing and the mounting-height window on that model. New York does not publish one statewide PIR height for all products.

Factory masks or opaque tape applied as the instructions allow can blank a segment that looks at a problem area. That is application of the listing. Painting the window, spraying it, or hanging a coat over the unit is not a mask; it is a coverage loss and may be a trouble or sabotage condition (section 11.3).

Look-down (creep) zones

A wall unit at listed height can have a dead cone on the floor at its base. An intruder who crawls the wall under the detector stays out of the main fans. Many security PIRs add look-down or creep zones — extra facets aimed steeply down — so that cone is protected. If the model includes look-down, the walk-test includes a pass under the unit. Taping those facets for the cat creates a bypass path the listing did not give you.

Pulse count

Pulse count (pulse processing) is a sensitivity trade, not a code number. One pulse alarms on a single zone crossing. Two or three pulses require additional crossings inside a short window. Higher count reduces alarms from a brief curtain flutter, a small animal at a zone edge, or a thermal spike. It also makes a fast, brief crossing less likely to report. 19 NYCRR Part 195 does not assign a statewide pulse number. You set what the instructions allow for that environment, then you prove catch with a walk-test.

White-light immunity (qualitative)

Many security PIRs carry a white-light immunity claim in the listing: headlights, camera flashes, or a brief lamp burst should not, by themselves, be enough to alarm. Treat that as a qualitative listing feature, not as permission to aim the lens at untreated west glass all afternoon. Direct sun on the window, moving shadows of hot blinds, and heat pouring through glass still create contrast the pyroelectric pair can see. White-light immunity is about visible-light transients; it does not repeal temperature-contrast physics. Do not recite a lux number as if it were in the DOS bulletin.

Security PIR versus fire occupancy sensors

Lighting occupancy and vacancy sensors often use PIR (sometimes microwave or dual-tech) to switch lights or HVAC. Those products are not the motion detectors this chapter is about. They follow energy or lighting application rules, with different listings, timeouts, and usually no burglar-alarm reporting. A fire-alarm smoke or heat detector is a different initiating device; Module 4 covers those. On this exam, motion detector, PIR, interior trap, and space protection mean security intrusion.

Exam traps

• Passive does not mean battery-only or unpowered.
• Emitting an infrared beam describes some active IR beams, not a PIR.
• A PIR that fails to report in a uniform-temperature space is physics.
• An occupancy lighting sensor is a distractor when the question is licensed alarm installation.
• 195.1(d) and 195.1(e) name motion detectors again under maintaining (inspection and testing to prevent problems) and servicing (repair, troubleshooting, replacement). Installing, inspecting, or replacing a PIR on a security system is licensed work.

When you walk a Buffalo ranch or a Brooklyn storefront, the PIR is the interior trap that still catches movement after a door contact is bypassed. You choose volumetric versus curtain from the listing, you keep contrast in mind, you leave look-down intact unless the instructions allow a specific mask, and you set pulse count for the room — then you prove it with a walk-test in section 11.3.