A motion sensor is a crucial element in security systems, automatic lighting setups, automatic doors and many more applications.
As their name suggests, they primarily detect motion.
There are many different types of motion sensors available that are set off using different types of technology.
The most common types include Infrared and Microwave.
Sometimes, motion sensors can be set off unwantedly, which can be quite an annoyance.
But, can wind set off a motion sensor? Wind cannot set off a motion sensor by itself. However, there are certain instances when wind can play a role in setting off a motion sensor. With an infrared sensor, if light is shining through trees onto the motion sensor, wind can set off the motion sensor when it blows the leaves causing a change in light levels.
With an microwave type motion sensor, if an object is blown past the motion sensor due to high winds, this can cause the motion sensor to be set off.
The different types of motion sensors
When it comes to motion sensors, you have a variety of them to choose from. Each having their own advantages and disadvantages.
Choosing the right one depends on the application you will use them for and how well it performs in that application opposed to the other types of motion sensor.
The first most common type is the Passive Infrared (PIR) motion sensor.
This type of motion sensor gets set off by detecting heat (infrared energy) given off by humans, animals, and anything else with a heat signature.
It is important to note that only changes in temperature will set off a PIR motion sensor, not constant temperature.
This type of motion sensor is mostly found in home security systems.
The next most common type of motion sensor uses Microwave technology.
A microwave motion sensor uses electromagnetic microwave pulses that are emitted from the transmitter of the motion sensor which are then reflected off humans, animals, objects etc and reflected back to the receiver of the motion sensor.
Other types of motion sensor available include;
- Dual Technology (combination of PIR and Microwave)
- Ultrasonic
- Vibration
How a motion sensor gets set off
Now that we know the most common types of motion sensor, let’s take a closer look at how they get set off (we will concentrate on the PIR and Microwave sensor).
Knowing how they get set off will give you a better understanding of how wind cannot directly set off a motion sensor, but can influence objects around it to set them off.
How an Passive Infrared Motion sensor gets set off
A PIR motion detector contains two slots which are made of material capable of detecting Infrared energy.
A PIR motion detector that is not detecting any motion, it is said to be idle. In this state, both slots detect the same amounts of Infrared energy.
When a body like a human or animal moves in front of the PIR detector, it will cross one half of the PIR sensor which causes a positive differential change between the two slots.
This is what sets off the PIR motion sensor.
A note should be made that a change in ambient temperature will not set off the motion detector as both slots will see the same change in temperature. Only when there is positive differential change between the two slots will the PIR motion detector be set off.
This type of sensor does not emit any infrared beam and is why it is known as Passive Infrared.
How a Microwave motion sensor gets set off
This type of motion detector uses electro-magnetic radiation to detect motion.
An electro-magnetic wave is sent (through a transmitter), which then bounces off objects and is reflected back to the receiver.
The receiver can use this information to see whether an object is moving within a given space or not.
If an object is moving, the reflected wave is altered in its return time.
If an object is stationary however, the reflected wave will return back to the receiver at the same rate.
A great capability of a Microwave motion detector is that it can tell if an object is moving towards or away from it, not just past it.
How can wind set off a motion sensor?
Now that we know how each type of sensor gets set off, let’s see how wind can affect a motion sensor and set it off.
First the PIR motion sensor.
So how can wind set off a PIR motion sensor?
Sunlight, like most other light, contains infrared energy.
If placed outside, direct sunlight should not be much of a problem when it comes to setting off the motion sensor as we need a positive differential change to set it off.
However, if the sunlight is shining onto the PIR motion sensor through trees, this is where wind could play a part in setting off the motion sensor.
As, we know that a PIR motion sensor detects movement through changes in infrared levels.
If the light shining onto the motion sensor through trees is disrupted by wind, it could cause a change in temperature, thereby setting off the motion sensor.
It doesn’t have to be a tree, it could be any object that is blocking the light but can be swayed by the wind.
When it comes to the microwave motion sensor, the concept is similar however, it does not involve the obstruction of light.
Since microwave motion detectors are set off purely by motion, for it to be set off indirectly by wind, the object will have to be moved by the wind inside the motion sensors Field of View (FOV).
Say, for example, a rubbish bin is moved by the wind in front of the microwave motion detector, it will be set off as there was movement that altered the return time of the microwave signal.
So you can see, that wind does not directly set off a motion sensor, but does so indirectly by moving objects which the motion sensor perceives as movement.
How to avoid a motion sensor being set off by a wind
Having a motion sensor that gets set off unwantedly is an ‘unwanted’ situation.
There are a couple of factors that can help you lower the chance of your motion sensor being falsely set off by the wind which include Placement and Sensitivity.
Placement of your motion sensor means that you mount it in a spot that does not have direct sunlight through trees where wind can alter light levels.
When checking the ideal spot, observe sunlight later in the evening when the sun is lower in the sky (because when the sun is overhead it should not be much of an issue).
You could also place it in corners under coverings, where sunlight does not get too easily.
With microwave motion sensors, your best option is to ensure your surroundings are clear of objects that can be easily moved by the wind.
Sensitivity of your motion sensor involves increasing its sensitivity. Every (if not most) motion sensor has the ability to modify the levels at which it gets set off.
Increasing the sensitivity means that it will take greater levels of Infrared (for a PIR sensor) or greater movement (for a Microwave sensor) to be set off.
Lowering the sensitivity does the opposite.
So, if you increase the sensitivity of your motion sensor, it will lower the chance of wind being able to set it off.
Could wind set off motion sensors that are installed indoors?
There might arise situations where wind could set your motion sensor, even if it is indoors.
As you know houses have windows, and light has the ability to travel through windows. So, the same issue with light shining through trees and disrupted by wind blowing the leaves could occur indoors.
Again, to combat this, place your motion sensor in spots where light does not shine and cause any disruption.
