PIR Sensors: What they are & where to put them

Passive Infrared (PIR) sensors have become a key component of smart alarm systems. Here we run through what they are and where they should be placed to keep even the most light-footed thieves at bay.

boundary pir sensor

What are PIRs?

Passive Infrared sensors work by detecting body heat, or infrared energy.

The sensor views the room as a grid. If it senses a movement of a certain temperature, it will interpret this as an intruder.

Premium PIRs, like Boundary’s, can scan for a heartbeat to verify that the movement comes from a living being.

One sensors are also engineered to minimise false alarms caused by pets by disregarding movements under a specified weight. Boundary’s sensor ignores any weight lower than 35kg. It’s also sealed against insects. So you don’t have to worry about the police showing up to arrest a bug.

Where to place your sensor

  • Corners

The best place to fit a PIR is in the corner of a room. This ensures maximum coverage of the space as the device maps out its grid.

  • Choke-points

Choke-points are areas that an intruder would have to walk through and so should be prioritised when installing PIRs. These could be entry doors or hallways.

  • Upstairs

It’s easy to fall into the trap of keeping your security airtight downstairs whilst neglecting the upper floors. Intruders may enter through an upstairs window and so having PIRs installed at key choke-points on all floors can help secure against climbers.

  • Visible from windows

Perhaps the most important thing to consider when deciding where to put your PIRs is whether they are visible from windows. Detecting an intruder is important but deterring them in the first place is better.

Where not to place your sensor

  • Above a heat source

As PIRs work by detecting body heat, a rise in temperature caused by radiators or boilers can confuse the system and affect accuracy.

  • The conservatory

When the sun shines the raised temperature in a conservatory will have a similar effect to a warm radiator, possibly triggering the sensor unnecessarily. Instead, place your PIR at the choke-point between the conservatory and its adjoining room.

  • The bathroom

Over time, the steam from showers and baths could reduce your sensor’s sensitivity. PIRs should be installed where they will stay dry and won’t be subject to rapid changes in temperature.

Motion sensors are the preserve of motion pictures no more. You’re probably already used to them opening automatic doors at the supermarket or even turning the tap on in a high-end restaurant bathroom. When used correctly, home security can also be enhanced by this technology.