The detector, the sounder and the light, at the same point on the ceiling.

The normal thing in a detection system is for each thing to be an element: the detector on the ceiling, the sounder on the wall, the light for where there is noise. Each with its place, its cable and its hole. This family works with elements that bring the sensor, the sounder and the indicator light together in one body hanging off the loop.

The effect is not aesthetic. Fewer elements means fewer holes drilled, fewer metres of cable and less time on site, and that decides whole projects in a listed building, in a hospital that cannot close a storey or in a refurbishment where the ceiling is the one you have.

You come across it in hospitals, schools and universities, government buildings, museums and buildings with heritage protection, airports and care homes. Places where there are people who do not evacuate on their own and where the building work is as much of a nuisance as it is a cost.

The panel takes cards, and out of each one comes an addressable loop that goes out and comes back: every element has its own address, so the screen says which point has fired and not which part of the building. With isolators spread along the run, a short circuit eats one section and not the loop.

Here there is a decision no other system has, and it is the price of the good idea: if the sounders hang off the loop, the loop has to give them current when they all sound at once. That sets how many elements fit, what cable cross-section is needed and what batteries the panel calls for to hold up with no mains. It is calculated in the design with what is actually going to be fitted, and recalculated every time somebody extends it. The extension nobody recalculated is the most repeated fault in this type of installation.

On detectors, the usual and with the same criterion: optical in offices, corridors, rooms and suspended ceilings with cable; heat in kitchens, car parks and plant rooms; multi-criteria where you need the sensitivity of the optical one in an environment that is not clean; flame outdoors and in tall industrial units; aspirating detection when the ceiling is twelve metres up or you have to find out very early, as in a server room.

And warning people, which in these buildings is half the work. Call points next to the exits, sound spread around and voice evacuation when you have to say something more than «get out»: in a hospital or a tall building you do not empty everything at once, you empty it in parts and in an order, and that is said with a voice and not with a sounder. The rest of the building goes with it: smoke doors closing, turnstiles and barriers releasing, air conditioning stopping, lifts coming down.

The panel keeps the value each sensor sends and how it changes, so it knows which one is getting dirty and warns before it starts giving false alerts. That turns the inspection into something targeted: what asks for cleaning gets cleaned, and you know which point of the building makes the detectors dirty fastest — which is almost always a clue to something.

What no adjustment fixes is a detector in the wrong place. An optical detector at the air outlet of a kitchen, next to a welding area, on a loading bay with forklifts or in a changing room with steam is going to go off until somebody disables it. And a disabled detector is still drawn on the plan, which is the worst possible combination: the risk is uncovered and the documentation says it is not.

There is a detail peculiar to this type of system: when the sound is spread over many small points, the risk is not that it cannot be heard in the corridor, it is that it cannot be heard inside a room with the door closed and the television on. That is not checked on a drawing. It is checked by measuring, door closed, in the worst rooms.

It fits where the building work is the problem: buildings in use, listed buildings, phased refurbishments, storeys that cannot be closed. It fits where evacuation in parts and with a voice is needed. And it fits where it suits you to have sound at every point instead of four big sounders badly shared out.

It does not fit if what you have is an open industrial unit with few points: there, bringing three things together in one saves nothing and the loop calculation becomes the complicated part of a simple project. Nor does it fit if the building is going to grow a lot and nobody is going to recalculate anything: this system rewards order and punishes extensions done by eye.

Everything electrical and electronic falls inside it: the detection design, the control panel, the loops, the elements, the voice evacuation, the interlocks with the rest of the building, the commissioning and the maintenance. End to end and with no intermediaries.

The water does not. Sprinklers, fire hose reels, dry risers, pump sets, tanks: another licence, other trades, another line of work. In a hospital or a school there are almost always both halves, and we say so in the first meeting so the budget counts on both companies from the start and the hole does not turn up halfway through the works. Of the gas fire suppression we do the electronic part —detection, delay, warnings, release, abort and interlocks— and not the cylinder bank or its pipework.

Your people have to be able to silence, reset, read the history —at what time, which point, what happened before— and understand a fault alert without calling anybody. In buildings with phased evacuation there is something more to teach, and it is what is really at stake: who gives the order to go from warning one storey to evacuating the building, and on what criterion.

Temporarily disabling a zone is taught as well, because it happens every week: building work, welding, a two-week refurbishment, a room where somebody has let the steam out. It is taught with its written rule and its record of who disables and who puts it back, because if it is not taught somebody is going to solve it by disconnecting something, and that leaves no trace.

Adding or moving elements, changing the programming, touching sensitivities or updating the panel is not handled by your people, and not because they do not know how: a detection installation is maintained from a company licensed to do it, and what gets done is signed off in a file. What does decide whether they really operate it is the drawings of what is there, the one-page procedure and training by role: the night shift and the maintenance manager do not need the same session.