Most people arrive at this question holding a list. Three motion detectors, a couple of glass breaks, contacts on the exterior doors, a keypad by the back entrance. Somebody produced that list, and the reasonable-sounding question about it is which brand of motion detector is the good one.
That is the wrong question, and it is wrong in a way that costs money quietly for years.
A detector does not protect a building. A sequence of detectors does, and the sequence has a shape. Every intrusion into a commercial building passes through the same four stages: someone reaches the building, someone gets through an opening in its skin, someone moves around inside it, and someone reaches the thing they came for. Detection is the business of noticing that progression — so the useful question is not "is this a good detector" but "at which of those four stages would we currently find out?"
Ask it that way and something uncomfortable usually surfaces immediately.
The four layers
Perimeter is everything that tells you somebody has reached the building — the yard, the compound, the lot, the loading area, the roofline, the fence. Detection here is early, which is its whole value: it is the only layer that gives you time before anything is damaged.
Openings are the doors and windows themselves — the skin of the building. This layer answers a narrower question: has the envelope been breached, and where? Magnetic contacts cover the doors that open; glass break detection covers the panes that don't.
Interior volume is the space inside. Motion detection lives here, and it is the layer that catches everything the first two missed — the person who came through a route nobody anticipated, the person who was inside before you locked up, the roof hatch that isn't on anyone's list.
Asset is the specific thing worth protecting. Not the room it lives in — the thing. The safe. The stock cage. The tool crib. The server rack. The pharmacy cabinet. The reel of copper. Detection at this layer is deliberately narrow, and that narrowness is a feature: it is nearly impossible to trip by accident, and if it goes off, something is genuinely happening.
Those four are not a ranking. Each answers a different question: perimeter answers when, openings answer where, volume answers is anyone actually in there, asset answers are they at the thing that matters.
The failure mode is imbalance, not cheapness
Here is the pattern we see repeatedly in buildings that are disappointed by their systems, and it is almost never about the quality of the equipment.
A warehouse has eleven motion detectors and no perimeter detection at all. Everything is discovered at the moment somebody is already walking around inside, which means the response starts from zero with the intruder already past the goods.
A retail unit has contacts on every door in the building — front, back, stockroom, staff — and nothing watching a display window that fronts directly onto a street. The doors are exhaustively detected. Nobody is going to use a door.
An office suite has a well-designed interior layer and nothing at all on the server room, so a system that would happily report somebody crossing reception cannot tell you anybody reached the one cabinet in the building holding client data.
In all three cases the equipment is fine. The design is lopsided. Somebody added detectors in the layer that was easiest to add detectors to, and the building has a thin layer nobody has examined because nothing in the quote ever named it.
This is why "which detector is best" is the wrong question. A fifth motion detector in a room that already has four is worth close to nothing; a first detector in a layer that has none changes the outcome of an entire incident. The right question is which layer are we thin in? — and you can answer it on a walk around your own building without knowing a single product name.
Working the layers, one at a time
Perimeter: earliness is the product
The reason to detect at the perimeter is time. Everything else is downstream of that.
Outdoor detection is also the hardest environment on the site, and in coastal BC it is a specific kind of hard: rain, wind-driven debris, fog, the low winter sun sitting in a sensor's field for an hour a day, and freeze-thaw cycles that move mountings. Photoelectric beams in Canadian winter conditions is its own subject for exactly that reason — the outdoor layer is where a badly chosen device produces the most nuisance activations, and nuisance activations are what get a layer switched off.
The judgement call here is honest scope. A perimeter layer that covers the two approaches anybody actually uses, and is trusted, beats one that covers everything and gets bypassed every night because it cries wolf.
Openings: two different physics, two different jobs
Doors and windows are one layer but two mechanisms.
A magnetic contact detects that a door or window has opened. It is the simplest device in the building and among the most reliable, and its limitation is exactly as narrow as its function: a contact on a window says nothing whatever about the glass in that window. Break the pane and leave the frame shut and the contact is still perfectly happy.
That is the gap glass break detection exists to close, and glazing is where this layer gets genuinely technical — see below.
A contact also only tells you the truth if the wire between it and the panel is being watched. That is what end-of-line resistors and supervised loops do, and it is the difference between a device that reports a fault and a device that goes quiet in a way nobody notices.
Interior volume: where dual-tech earns its place
Motion detection is the layer with the most product choice and the most disappointment, because it is the layer most exposed to the ordinary life of a building.
Passive infrared detectors respond to moving thermal contrast crossing their pattern, which is why a heat vent cycling on, a hanging sign turning in the draught, or the sun tracking across a floor can all look like a person. That is not a defect; it is the physics of the device meeting the reality of a room.
Dual-technology detectors address this by requiring two independent physical phenomena to agree before an alarm is declared. The trade is straightforward and worth stating plainly: you get fewer nuisance activations and, because both technologies must agree, a harder detection requirement. That trade is excellent value in a warehouse with radiant heaters, a room with roll-up doors, or a space with air handling running overnight. It is often unnecessary in a quiet sealed office where a single technology behaves itself perfectly well.
Which is the real point: dual-tech is not the upgrade tier. It is the right answer in hostile rooms and an overspend in calm ones. A building is usually a mix of both.
Asset: the layer that gets skipped
The asset layer is the one most often absent, and it is the cheapest of the four to add because it protects one object rather than a volume.
A safe, a vault or a stock cage can be watched directly by seismic detection, which listens for the structure-borne signature of an attack on the body of the thing itself rather than for a person in the room. That is a different kind of evidence, and it means detection does not depend on the intruder having tripped anything on the way in — which matters more than people expect, because the ways in that nobody planned for are the ways in that get used.
If your building has an identifiable "the thing" — and most do — ask what happens if somebody reaches it without crossing anything else. If the answer is "nothing", you have found your thin layer.
Two BC realities that change the design
Nuisance alarms are a financial problem here, not an irritation
In much of the Lower Mainland, an unreliable detector is not merely annoying — it is billable. False alarm charging is municipal, and the models differ structurally from city to city. Burnaby's consolidated fee schedule allows the first two false alarms in a calendar year free, then charges $225.00 for the third, $300.00 for the fourth, and $400.00 for the fifth and each subsequent one. Surrey does not work by count at all: its fee-setting bylaw charges $133.00 if the invoice is paid within fourteen days and $165.00 if it is paid after.
One flaky detector on a windy elevation is therefore not a maintenance ticket — it is a recurring line item with no ceiling, and in some municipalities it starts billing on the first event. The full picture, including Vancouver's quite different mechanism, is in false alarms and what they actually cost you in BC; confirm the figures against your own municipality's current fee bylaw before relying on them.
The point for detector selection is this: reliability is a budget item. Specifying a more discriminating device in a difficult room, or declining to put a detector somewhere it cannot behave, is not gold-plating. It is avoiding a charge.
Modern commercial glazing is not the glass these detectors were conceived for
Acoustic glass break detection works by recognizing the sound signature of glass failing. Everything about its performance therefore depends on what the pane does acoustically when it breaks — and modern commercial glazing does not behave like a plain single sheet.
Sealed insulating units, laminated glass, and coated or filmed glazing all change how the break sounds and how much of that sound reaches the detector. Two panes with a sealed cavity between them are not one pane. A laminated interlayer does not release energy the way an unlaminated sheet does. A film applied after the fact changes the pane again, and it appears in none of the drawings you hold.
The practical consequences are real and they cut two ways: the type of detector appropriate for the glazing may not be the acoustic one at all, and where an acoustic detector is appropriate, the coverage distance it can be trusted over is reduced relative to plain glass.
We are not going to give you a number here, and you should be sceptical of anyone who gives you one without naming a document. The derating for a particular glazing construction comes from the detector manufacturer's own published data for that construction — the spacing table in the installation instructions — and it is product-specific and glazing-specific. A figure quoted with no product and no source attached is a figure somebody remembered.
So the question to put to your integrator is narrow and answerable: what is the glazing construction on this elevation, and what does the manufacturer's data say the coverage is for that construction with this detector? An installer who works with commercial glazing will reach for the instructions. One who answers from memory has told you something useful.
The last point, and the one that actually decays
A system detects what it was detecting on the day it was commissioned. Not what it was designed to detect — what it was verified to detect, by somebody walking the space and watching the panel respond.
And then the building changes. Racking goes up and a motion detector now watches the side of a pallet. A tenant improvement puts a partition through the middle of a pattern. A window gets filmed. Stock is stacked to the ceiling in the aisle the detector was aimed down. None of these generates a fault. The panel arms cleanly, the keypad says READY, and the coverage you paid for is quietly gone. That is the most dangerous condition a security system can be in, because it looks exactly like a working one.
Walk-test annually, and again after any change to a room's layout. Have the results recorded per device, with a date. It is the cheapest thing in this entire article and it is the only one that tells you whether the other four layers are still true.
