Passive Infra-Red (PIR) sensors are really important in the contextual smart home. They are great source of timely and accurate occupancy data, down to zone or room level and sometimes to an area within a room. They detect the infra-red 'heat' from people and animals and use this to detect movement (they are sometimes referred to as motion sensors). There are many different types available to provide different ranges, field of view, etc. Some are optimised to ignore smaller objects moving, such as pets. It is therefore important that you choose a PIR sensor for each environment and use case carefully.
PIR sensors in our @smartest_home are always active and sending events to our Home Control System. There is no need for the concept of them being 'armed' or 'disarmed'. A contextual smart home will just know what it needs to do with each event and what action to take (if any). They are also not installed to address just one function, such as lighting control. Each PIR can be used by the contextual smart home to do many things, making them much more valuable.
You need to choose a PIR sensor for each application or set of applications. Each make & model will have a different range and field of view, both in the vertical and horizontal planes. Some also have configurable pulse counts (how much much activity or motion they must 'see' before they trigger). For external use, you really will need IP44 rated sensors but you can get away with internal ones if they are sheltered. It really depends on the quality of the design and the materials.
Where you mount it a PIR also a big factor in how well it will work. They are generally more responsive to people walking across the field of view and not towards them. Wired PIR sensors are a LOT cheaper than the equivalent wireless sensor and will generally perform better, with much lower latency. All PIR sensors need to be rigidly mounted. If they can be moved by things like the wind, then may be falsely triggered. They can also be falsely triggered by things moving in front of them. You shouldn't install them pointing towards a window or a radiator.
Most of the PIR sensors in our home are these Quest wired 12V PIR sensors, which use just 15mA in standby. They are very reliable (some have been in our home for 14+ years), easy to use and cost just £6 each. They provide a 12m range and a 110° field of view. They have an internal jumper, which is used to configure the pulse count (1, 2 or 3) and this enables some sensitivity adjustment of sorts. There is also an internal jumper to enable/disable a red LED, which is used for set up and test. The LED is not meant to be visible in normal use!
These are basically standard PIR sensors as used in most security alarm systems. By connecting them to our Home Control System, we are making them very smart. This is a good example of how you can re-use equipment that may have already been installed in your home.
We also use these much smaller and cheaper wired 12V PIR sensors. They are available in black and white. This makes for a very subtle installation and performance is good. These sensors have an in-built delay of about 6 seconds between triggering, so they can only be used in certain applications.
The internal module can easily be extracted and used without the housing, meaning it can be used for very subtle installations. It is just 12mm in diameter. We have installed them in furniture and the structure of our home. Installed like this, they are practically invisible. The quality of wiring on these modules is variable. We solder new wires onto these modules before we install them and for clarity, we use colour coded wiring too.
This Arduino HC-SR505 PIR sensor is designed to work with 5V dc and is very compact. It has an on time of about 8 seconds but this is good enough for most occupancy applications. It is also very cheap at around £2.70 per sensor.
In some places it is not possible to run wires, so have have used wireless PIR sensors like this Fibaro FGMS-001 3-in-1 Z-Wave sensor. These are a huge compromise though. Being battery powered, they cannot report events at high frequency. Battery life is also quite short in places with high traffic. We have one of these where the batteries last less than 3 months.
This sensor also measures temperature but the reporting frequency is also low. It also measures light level.
It's really important that you use high quality external PIR sensors. Cheap sensors are prone to false triggering due to wind, moving plants and other objects.
We particularly like the GJD GJD020 'Opal XL' PIR sensor and use it extensively around our contextual smart home. We have undertaken a detailed review of this sensor.
PIR sensors for outside use need to be designed to withstand the harsher installation environment.
From the various smart home forums, we can see that lot of people are happy with PIR sensors generating events at quite long intervals apart, sometimes even several minutes apart. Whilst this is often down to the limitations of wireless PIR sensors, this is missing a big opportunity in the contextual smart home. Depending on the zones and size of each zone, we will report PIR events as little as 1 second apart and typically about 3 seconds apart. Whilst this generates a large number of events, our Home Control System can easily handle millions of events per day.
The main advantages of frequent events is that they can be used for many applications and services in the smart home. Our smart home can infer many things from the events and the event frequency, including activity levels, people counting and working out which direction people are moving through our smart home.
Some of our PIR sensors can generate many thousands of events each day.
