Motion sensors come in many devices, and accidentally triggering one can be frustrating and even stressful. I set out to figure out why Motion Sensors get triggered, and if something as simple as turning on a light can set one-off. Here’s what I found.
Lights can trigger a Motion Sensor. For Motion Sensors which sense Infrared Radiation, lights which quickly change in temperature can cause the sensor to trigger. Motion sensors which use image comparison can also be set off by light when a sudden change in light intensity occurs rapidly.
What I found in my research was that there are many different types of Motion Sensors. Not that they look any different (most are hidden within another device after all) but that they function differently in how they detect motion.
While lights can only set off a Motion Sensor using IR (Infrared), there are other ways to accidentally trigger IR Motion Sensors and just about every other type as well.
If you want to either prevent accidental triggers or learn how to stop them if they’re already happening with your setup, keep on reading!
WHY DO LIGHTS TRIGGER A MOTION SENSOR?
As I briefly mentioned before, lights and light bulbs will only impact one type of Motion detector and potentially set off a false alarm.
These motion sensors look for changes in Infrared Radiation to decide whether or not there is motion. Infrared Radiation is also known as heat.
Most passive Motion Sensors are going to use this sort of technology.
Built-in detectors on floodlights outside your house, inside your house, even some alarms and small cameras are equipped to detect IR.
But why do Lights have the ability to trigger one of these sensors?
Motion sensors which detect IR can “see” the heat which comes from a light bulb.
If the motion sensor detects a rapid change in that heat, whether it’s the location or the intensity, it will determine that motion is happening (or has happened) and will trigger whatever is being triggered.
Lights which get very hot can cause trouble because of the way these sensors function.
If you’ve ever touched an older light, like an incandescent or CFL (Compact Fluorescent Lamp), once they’ve been turned on for a while, they can get pretty darn hot!
The wattage of the bulb determines how much power (and therefore heat/ IR) travel through it when running.
Higher wattage means that a higher amount of power is traveling through the light, and that leads to more energy available to turn into heat.
How much of that wattage gets turned into heat depends on the efficiency of the light.
LED bulbs are generally more efficient, and get less hot
Giving them a few minutes to cool down is more than a suggestion…it’s a necessity!
Even with a hot bulb, Motion Sensors are triggered when they think there is some living thing moving in front of them.
For light to set off the sensor, it has to heat up very quickly. So quickly, that it looks like something warm-blooded just appeared in a spot where a second ago there was nothing.
Some light bulbs will either emit a low amount of heat (low wattage LED bulbs) or take quite a long time to reach their maximum temp.
In this case, the change in heat is so low or so gradual, it’s probably not going to cause any issues.
So now you know about one type of motion sensor and how it works (Infrared Radiation), but what about the other types? Are they sensitive to light as well?
What are the types of Motion Sensors?
There are a few alternatives to IR sensors, and the first one is probably just as common, if not even more common these days!
Many hidden cameras are programmed to repeatedly take photo after photo and compare them to look for differences.
Even your cellphone can be programmed to work this way, you might notice how the screen turns on when you look at it? That’s motion detection in away.
If the camera senses that it’s being held still, it will look for the differences between each photo, comparing pixel values to see if there are changes in the color levels.
If there are, the camera then “senses” motion, and can be further programmed to start taking video or send the pictures to your phone or email.
To save space, these sensors will often delete the photos if there are no differences found, and then keep rotating through that cycle of capture, compare, react, delete, repeat!
Since these kinds of sensor rely on comparing images, they need to have some sort of consistent light source to work properly.
When you suddenly turn on the light in a dark room, or there is a bright flash of light, that will cause the camera to sense a dramatic change in the image (one being dark and the next frame being much brighter), which will often cause this sensor to trigger.
What Are Active Sensors?
The next type of sensor you’re probably familiar with is one which is used in elevators and grocery store doors all around the world.
These are called “active” sensors because they emit a beam of light, sometimes IR, and then look for a change or break in that beam.
Another great example is the laser tripwires in spy movies!
You know, the ones the spy has to spray to make visible and then bend over backward to avoid?
When one of these beams is interrupted or distorted, that can trigger the alarm to go off (or whatever device is hooked up).
These types of sensors are pretty robust to light changes, as their honed in on the light they emit, so it’s likely that they won’t be affected or triggered by light.
What Are Ultrasonic Sensors?
Ultrasonic sensors are those which use waves of sound to detect motion or activity.
Like little radars or an ultrasound, these units emit sound waves and look for patterns in them when they bounce back to see if something is moving.
Bats also use this type of mechanism to see in the dark!
If you really want to get fancy, you can get a system using Doppler, which on top of being able to detect motion, can also tell you the speed and direction of the motion.
Just like watching a storm system move across the state, you could see an image moving across your front lawn!
Because sound is not impacted by light, and there is not a way to detect light in these setups, the light will not trigger an ultrasonic motion detector.
Finally, there are the most sophisticated sensors of the lot.
These sensors, called electro-capacitive or electric field sensors, work just like the screen in your smartphone.
They detect changes in electric fields, which indicate the motion of some kind.
Sharks use the same technology to detect prey when they’re hunting.
The nifty thing about this type of sensor is that it can be used through structures like walls or doors.
These aren’t entirely common, but they are available in some devices such as Barking Dog Alarms or Hotel Door Alarms, perfect for situations when you need to see on the other side of your door.
Here’s a great example of a Barking Dog Alarm
Can Wind Set Off a Motion Detector?
The wind itself cannot Set Off a Motion Detector directly, but it can cause other objects to move. These moving objects will then cause the Motion Sensor to trigger.
If you’re worried about wind movement, consider where your sensor is being placed.
Living in a windy environment means that having a sensor outside is going to expose you to potential false alarms.
A big pile of leaves can become a storm of movement when hit by a gust of wind.
Inside, your air vents can be a major source of wind, and so can opening and closing your door.
Things close to these two, and even to an open window, are potentially going to be moved and trigger a sensor.
The sensitivity of your sensor also matters, because small movements like a curtain blowing might trigger some setups, while others will just ignore it completely.
How Do You Stop a Motion Sensor Light From Turning On?
To stop a Motion Sensor Light from turning on, the easiest solution is to cut all power going to the unit.
This is effective if you simply want to make sure the sensor doesn’t trigger, like if you’re going to be moving in front of the sensor a lot (moving mulch outdoors or doing yard work in front of a camera for example).
This can be accomplished by switching off the power to an outlet, or flipping a breaker if the unit is hardwired into your house.
If you want to override your Motion Sensor and have manual control of when it goes off – this might be the case with something like a motion-activated floodlight – it will depend on your make and model.
Some models have a switch sequence which can override function and turn the unit on or off.
Turning a switch on and off quickly, often less than 1 second, will cause the unit to enter a manual override mode.
In the case of the floodlight, this can cause the light to stay on or off until you reset the unit, or until a pre-determined time is hit.
For specific instructions on your sensor and to see whether or not it has this functionality, always check your user manual!