A motion detector (also known as a motion sensor), is a type of sensor that is used to detect motion which a Central Processing Unit like a Microprocessor or Microctroller can then perform a set of actions accordingly.
But, what kind of things can set off a motion detector? The most commonly used motion detectors utilise Passive Infrared (PIR) technology to detect motion. This means that they can detect the motion of a moving object that emits infrared energy. This means that anything that emits high enough levels of infrared energy as well as a change in temperature can set off the motion detector which can include:
- Humans
- Animals
- Heaters
- Sunlight
There are other types of motion detectors available which are used to detect motion. I will cover them and what sets them off in this article. The PIR type motion detector is just the most common.
How does a motion detector get set off?
Motion detectors come in a variety of designs which can get set off using different types of technology. You have a choice of different types of motion detectors available to perform the same job of detecting motion.
I will quickly discuss each type of sensor and how each gets set off and detects motion.
Motion detector type #1 : Passive Infrared
The first of the motion detectors is the Passive Infrared (PIR) detector. This is the most common type of motion detector used in home security systems and automatic lighting systems.
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 detector.
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.
What can set off a Passive Infrared motion detector?
Since the PIR motion detector is set off by a change in temperature, below is a list of bodies, objects that can potentially set if off:
- Humans
- Animals (Including insects)
- Heater
- Sunlight (if there is a change in light levels and temperature)
- Automobiles driving past
- Fire
Motion detector type #2 : Microwave
The Microwave motion detector is next on the list.
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.
What can set off a Microwave motion detector?
A microwave motion detector will be set off purely by things in motion (not a change in temperature), as this is what alters the waves emitted by the detector.
So things that can set off a microwave motion detector include:
- Humans in motion
- Animals motion
- Objects thrown in front of the motion detector
- Curtains moved by the wind
- Automobiles
- Basically anything in motion
Motion detector type #3 : Ultrasonic
Next we have the Ultrasonic motion detector.
A Ultrasonic motion detector works in similar principle to the Microwave motion detector.
However, instead of emitting a microwave, it emits a sound wave of very high frequency (above the hearing capabilities of humans).
The Ultrasonic Motion Detector’s transmitter first sends a sound wave. When that wave encounters bodies,objects, etc, it gets reflected back to the detector’s receiver which will calculate the time it took.
Much like the microwave, if the wave’s return time is altered, this is an indication of motion.
What can set off a Ultrasonic motion detector?
Since the ultrasonic motion detector detects motion in a similar fashion to the microwave motion detector, the things that can set it off are purely things that are in motion and modify the wave of the ultrasonic motion detector.
These things include, movement of humans, animals, objects etc.
Motion detector type #4 : Vibration
As the name suggests, vibration motion detectors detect motion purely through vibration.
The simplest vibration motion detectors contain a sensor that has the ability to sense vibration. When a vibration occurs the vibration sensor is set off and lets the central processing unit know that motion has been detected.
What can set off a Vibration motion detector?
For a vibration motion detector to be set off, it will require a person, animal, object, etc to generate a vibration that is within its vibration sensitivity limits.
The disadvantage of this type of motion detector is that it requires a certain level of vibration to set it off. If a person is careful enough and tip toes their way around the motion detector it will not be set off.
Motion detector type #5 : Tomographic
Tomographic motion detectors consist of multiple nodes (of receivers) set up in a space. Radio waves pass from node to node that create a mesh like network (like a laser system that you see in the movies).
When there is a disturbance anywhere in the network of nodes (ie someone walking past, an object being thrown past etc), the motion detector is set off.
What can set off a Tomographic motion detector?
Things that can set off a tomographic motion detector include movement that breaks the path of the radio wave which can include humans, animals, objects (anything with considerable mass to break the path of the radio wave)
Motion detector type #6 : Video camera
Last on the list of the different types of motion detectors is a Video Camera Motion Detector.
This type of motion detector utilises a video camera and software to detect movement. It does not use any special sensor to detect infrared energy or emit any special waves.
When something moves in front of the video camera’s field of view, software then can detect changes in picture and thus motion is detected.
What can set off a Video camera motion detector?
To set off a video camera motion detector, the thing that is being detected needs to be big enough to be captured by the video camera and analysed by the software.
Again, only motion will set off a video camera motion detector.
Applications where a motion detector is used
We have established the different types of motion detector and how they can be set off which include infrared, sound, vibration and video camera.
But, what are the applications where motion detectors can be used?
Due to their operating principle of detecting infrared and motion, they are primarily used in applications where motion needs to be detected.
The first most common area motion detectors are used are security systems. You might have a security system installed where you currently live. It will no doubt utilise motion detectors in different rooms to detect motion.
A security system is vital in homes, businesses, etc, as it provides a way to keep your household and everything you own safe when you are not at home. If a burglar enters your home/business the motion detectors will be set off and trigger an alarm and your security company.
When set off, the motion detector can also be programmed to trigger a video camera to start capturing footage.
Another common and useful application where motion detectors are used include automatic lighting.
Imagine you are walking towards your house in the dark of night. Trying to walk with no illumination can be very hard.
Automatic lighting using a motion detector can ease your pain by illuminating the path to your home. Also, leaving the light on throughout the night can make a dent in your electricity bill. A motion detector will only turn on the light when it is set off.
Other applications of motion detectors include:
- Automatic ticket gates
- Automated toilet flushes
- Hand dryers
- Automatic doors
Can small insects and animals set off a motion detector?
When it comes to small insects and animals, the Passive Infrared (PIR) motion detector is more susceptible to being set off.
This comes down to the fact that all living things emit varying amounts of Infrared energy.
Obviously humans emit larger amounts of Infrared and therefore the chances of setting off a motion detector is higher.
For small animals or insects, they need to be much closer to the sensor and be within the motion detectors Field of View (FoV) to set it off.
If the small animal or insect is at a considerable distance from the PIR motion detector, it will not be set off as they do not emit high levels of infrared to trigger it.
How to prevent a motion detector being set off by small animals and insects
But, what if you want to eliminate or lower the chances of your motion detector being set off by small animals or insects completely. Is it possible?
There are ways that you can lower the chances of a motion detector being set off.
Dual Technology Motion Sensor
As the name suggests, this type of motion detector includes two types of motion detection; Infrared and Microwave/Ultrasound.
This will drastically reduce the chances of small animals and insects setting off the motion detector as it needs to both detect infrared and motion in order to be set off.
Placement of the Motion Detector
Even with dual technology motion detectors, if mounted in places that are easy to get to, or lower to the ground, this will still be set off.
Mounting motion detectors higher off the ground and in corners will reduce the chances of it being set off by animals and insects.
Lower Sensitivity
You might be wondering, what about creepy crawlies and insects that can fly and can get to any nook and cranny imaginable. Placement of a motion detector will not affect them.
Your best option here with PIR motion detectors is to reduce their sensitivity levels. However, this does not mean you are lowering the infrared level sensitivity. This means that the motion detector will require higher levels of infrared to be set off.
As small insects have lower levels of Infrared, lowering the sensitivity will reduce the chances of it being set off.
The great news is that a human intruder will still be able to set off the motion detector!
Can you change the sensitivity of the motion detector to not get set off so easily?
Yes. You can change the sensitivity levels of motion detectors so that it takes either higher levels of Infrared or movement in order to set them off.
Can a motion detector be set off by daylight?
Motion detectors that use Microwaves or Ultrasound, will not be affected by daylight as they use sound reflected off living things and objects to be set off.
The issue of a motion detector being set off unwantedly by light is with PIR type motion detectors.
As you know, PIR motion detectors get set off when there is a change in Infrared levels. Sunlight is a great source of Infrared energy.
If the PIR motion detector is exposed to a constant source of sunlight there should be much of an issue.
Problems arise when there is change in light level. Maybe the light is shining onto the motion detector through a tree. If a wind blows and causes leaves to disrupt the sunlight beam, this could set off the motion detector.
So, when placing your motion detector outside, make sure to mount it in a place where light levels are constant and do not have sudden changes.
Can a low battery set off a motion detector?
Another reason that a motion detector could be set off is because of low battery levels. This can cause false triggering.
Make sure to routinely check the battery levels of your motion detector and change it if required.
Also, invest in good quality batteries as cheaper batteries lose their charge much faster.
Can rain set off a motion detector?
While rain won’t set off a PIR type motion detector, it can set off motion detectors that detect motion using reflected waves such as the Microwave and Ultrasound motion detectors.
Falling rain will cause a disruption in the times of reflected waves thereby causing the motion detector to be set off.
To combat these either use PIR motion detectors outside or adjust the sensitivity of motion detectors that use reflected waves.
Can wind set off a motion detector?
While sound cannot be reflected off of wind and has no Infrared signature to affect a PIR motion detector, as we saw above, wind only plays a part when it alters an object’s paths to disrupt light levels.
So, wind itself cannot set off a motion detector, but it can set it off with its ability to move objects past the motion detector.
