Home Alarm Sensors by Rooms

Residential alarm sensor sizing

A home intrusion alarm usually mixes passive infrared (PIR) motion sensors, one for each perimeter room, with magnetic reed switches on every external door and window. Weak walls or glass panels may also get vibration sensors. The estimator leans on the conservative side with sensors = rooms + 2 × external_doors, counting one PIR per room and one magnetic contact per opening leaf.

For the system to be complete you'll also want a sounder (a 110–120 dB siren), a control panel with a backup battery, and, ideally, a link to a 24/7 monitoring company (Verisure, ADT, Prosegur, Brink’s) that sends a response team when the alarm trips. The wider retrofit and renovation rules fall under ABNT NBR 16280, and reputable makers like JFL, Intelbras, Paradox and DSC ship hardware certified to EN 50131 grade 2 for residential use.

Applications

Use it to budget a new install or an upgrade, to size the zones on the panel (a PIR or a reed group usually takes one zone each), to figure out battery autonomy (most panels hold 12–24 h on backup), and to compare monitoring contracts that bill per zone or per device.

FAQ

Do I need a magnetic sensor on every window? On the ground floor, yes, along with any window someone could reach from a balcony or rooftop. Upper floors with no outside access can lean on the room's PIR instead.

Will pets trigger PIR sensors? A standard PIR will go off on small mammals. Pick a pet-immune model rated for animals up to 25–35 kg and mount it at the right height, around 2.2 m, angled along the room’s long axis.

Wired or wireless? Wired runs more reliably and is harder to jam, but it tears into a finished home. For retrofits, wireless (RF 433 MHz or proprietary) is what most people use. Just check the sensor battery life, usually 3–5 years, and choose a panel that warns you when a battery is running low.