Do Motion Detectors Work In the Dark?

Motion detectors are indeed the lynchpin of home and business security systems. They detect and deter trespassers from accessing your property and alert you or the monitoring team. In addition, the gadgets operate 24/7 to guarantee maximum protection throughout.

These detectors use one or combine multiple technology forms to detect movement in the controlled zone. Then, they sound the alarm or turn on the lights after sensing motion, which scares the intruder.

Usually, motion detectors have certain placement and operational specifications to function optimally. For instance, ensure they have a wide field of view and adjust sensitivity settings accordingly. But homeowners are not assured of the devices’ functionality in multiple conditions, so they always ask: Do Motion Detectors Work In the Dark?

Motion detectors work in the dark as they do not rely on images and light to discern motion. Besides, their movement detection has nothing to do with how bright or dark the immediate area is.

Passive infrared motion detectors identify changes in the received infrared levels and ultrasonic ones detect changes in the wave field after emitting sound waves.

Further, microwave sensors detect a disturbance in emitted microwaves. As a result, they will capture movement and trigger the alarm without images and lights.

Understanding how various motion detectors work is essential as it helps know what to expect. So, read this write-up for more insight into these home security units. We will also learn how to install them and address frequently asked questions.

How Do Motion Detectors Work at Night?

Do Motion Detectors Work In the Dark?
Image of a Motion Sensor

Motion sensors work differently at night depending on the technology they use. For instance, passive infrared motion sensors work in darkness by detecting infrared radiations. They pick up heat changes across their field of view.

A PIR motion sensor triggers an alarm when a heat-emitting object enters the targeted area. In addition, the detector is efficient in complete darkness since it does not depend on light sources.

On the other hand, microwave-based or ultrasonic radiation-based sensors emit waves and receive reflections from moving objects. They pick wave reflections from objects moving in the field of view.

We also have older motion sensor models that use fresnel lenses to scatter light and activate a resistance-based sensor. Moving objects cause a quick change in the scattered light on the lens and the sensor’s resistance, ultimately triggering it. But these detectors are quite technical and are not commonly used today.

Generally, modern motion detectors work well in the dark. Microwave, ultrasonic, passive infrared, or dual technology sensors rely on waves emission and reception of heat or reflections from moving objects in the monitored area.

But remember, motion sensors can falsely trigger the alarm in the dark. So, let’s closely look at the primary types of motion sensors for more insight.

  • Ultrasonic and Microwave Sensors

These detectors emit waves and await reflections from moving objects. However, they are easier to fool as they pick up motion changes in their proximity. In addition, the sensor may never trigger the alarm if an object is stable without suspicious reflections.

Either way, ultrasonic and microwave sensors do not depend on light to operate at night. Therefore, they are a perfect choice for 24/7 home surveillance.

Nonetheless, be wary of false positives in a microwave sensor. A high sensitivity setting causes the device to pick up reflections from any object within its proximity. Also, complement the detectors with a passive infrared sensor. Otherwise, you’ll fall victim to frequent false alarms.

  • Passive Infrared Sensors

These detectors work at night by identifying infrared radiations. However, if the emitters are on low sensitivity settings or the mode is disabled, the sensor won’t detect anything in the dark. Hence, test the device in darkness to confirm that it works well.

The caveat around passive infrared detectors is their ability to work through glass. Infrared rays cannot pass through the glass, so the sensor will not pick up heat changes through it. Further, aiding the sensor with a glass-tampering device is better than placing it outdoors.

  • Dual-Technology Sensors

These motion detectors are among the safest home security options, especially in the dark and when you want a low false alarm rate. They combine features from passive infrared and microwave sensors. Therefore, an object has to move and emit heat to trigger the alarm in the dark.

Dual technology sensors do not work in darkness through glass barriers. Further, the passive infrared detector does not trigger even though the microwave one would. Both detectors have to be activated for the alarm to sound.

Do Lights Set Off Motion Detectors?

Unfortunately, lights can set off motion detectors, causing them to raise a false alarm. These sensors pick up infrared radiations or heat signals and trigger the alarm based on any changes.

Moreover, since lights release a significant energy amount as their state toggle, they easily activate a motion sensor. However, this aspect does not apply to all motion detectors. Light bulbs trigger passive sensors, not active ones.

Light sources dissipate infrared or energy radiations which are picked up by passive motion detectors. The light bulb causes a rapid change in the heat intensity and causes the sensor to trigger.

Thus, low-wattage bulbs may not trigger the detector since the temperature change is not enough to set it off.

It all boils down to the light source’s power consumption and heat generation. For instance, older fluorescent lamps get quite hot and need high wattage to operate. They drain more power and deliver a high light intensity.

So, place these lights away from your motion detector as they are a common source of false triggers.

On the other hand, LED bulbs are more energy efficient, deliver the same light amount, and generate less heat. Moreover, they are cheaper than incandescent bulbs, so you can place them closer to sensors without worrying about false alarms.

Lights can also trigger motion detectors if their sensitivity is low. Here, even the slightest radiation or movement causes the alarm to trigger. If your device was not installed by a professional, review its sensitivity to minimize false triggers.

How to Install Motion Detector

DIYers have it easier when installing motion sensors as wireless options have become standard. Better still, if you know how to operate a screwdriver, you can comfortably install a motion detector.

However, correctly install the motion sensor to guarantee optimal coverage and help avoid false alarms.

Below is a simple procedure to get you started.

  1. Unbox the Motion Detector

Motion Sensor kits often come with instructions and mounting hardware. So, assess them carefully and follow the directives. Also, if the detector has separate batteries, put them into the allocated slot.

  1. Decide on a Suitable Location

Always consider the most effective motion sensor placement before installation. For example, corners are an ideal place as it allows passive infrared sensors to cover most area. In addition, most motion detector designs have angled edges with screw holes to accommodate corner placement.

Mount the motion sensor high on the wall to guarantee the best coverage. However, avoid placing it over large furniture pieces like an entertainment center or bookshelf. Otherwise, the structures will limit the passive infrared radiation range.

Also, position the motion detector opposite the main entrance. This applies in every hallway or room to make it easy to detect trespassers right away.

  1. Mount the Detector

Passive infrared sensors are light, so you don’t have to stress about drywall anchors and studs. Besides, a standard screwdriver does the trick while you can speed up the process with an electric screwdriver or drill.

Most motion sensors have a mounting bracket popping off the main body to allow easy screwing. Screw the bracket into the wall, then clip the detector back in.

This procedure makes maintenance straightforward as you can take the detector off the wall. But remember that some infrared motion sensors need a full disassembly for mounting.

  1. Connect the Sensor to Your System

Follow the manufacturer’s directives to connect the detector to your unit. Further, most DIY systems walk you through this procedure, often using a mobile application or the main keypad. So, you accurately set up and adjust your motion sensors.

  1. Adjust the Motion Detection Settings

Most motion sensors have three primary systems to arm the unit. The first one is the In-Instant mode where all motion triggers an alarm. Next, we have the In-Entry-Delay mode that works with an entry delay but only when triggered by door contact.

But it can sound an instant alarm after detecting motion in the facility without door contact triggering.

Finally, we have the Interior-Follow-Up mode that works on an entry delay, but only after door contact triggers. Though the detector can still identify motion in the targeted zone without a door contact activation.

  1. Maintain the Motion Detector

Over time, dust and debris accumulate on the motion detector’s screen, interfering with the infrared energy detected. As a result, it becomes less effective at motion sensing. So, clean your motion detector at least once every few months with a slightly damp microfiber cloth.

If you want to paint a surface near the motion sensor, remove it first. Furthermore, if you get any paint on passive infrared motion sensors, you’ll need to replace it.

Here’s How to Install Motion Detector

Other additional considerations for installing motion detectors include

  • Don’t Block the Infrared

Motion detectors are usually like flashlights sending out light beams but with motion-sensing infrared energy waves, not light waves. Besides, just like light is brighter closer to the source, infrared radiation is more intense nearer the device and spreads out farther away.

A motion sensor’s waves cannot penetrate walls or other hard items like furniture. When setting up the device, imagine it like a light on a wall. Also, anything creating a shadow from the light position blocks the detector’s ability to cover the shadowed region.

  • Consider Your Pet’s Size

Thankfully, we have pet immune motion sensors that prevent pet-related alarm triggers. However, these devices use ratings related to the animal’s weight and size. Thus, evaluating your pet’s size and activity is prudent to minimize false triggers.

Still, small pets can activate the sensor with enough verticality, especially if they like to practice their high jump. This aspect affects active sensors at the bottom of the stairs. The sensor views the pet like a mouse but as it approaches the device, it may appear like an elephant.

  • Overhangs Decrease Range

Installing motion detectors under an overhang, such as a carport, reduces their range. Just like your vision field decreases when you wear a hat with a brim or a visor, overhangs block the gadget’s light’s 180-degree sensing angle.

  • Motion-Sensing Light Switches Are Not All Equal

Motion detection switches work differently, requiring you to aim for the most suitable device for outdoor or indoor use. For instance, an occupancy detector automatically turns on when you enter a room and goes off when you leave.

On the other hand, vacancy sensors turn off the lights in empty rooms but you have to turn them on when you enter. Further, dimmer sensors are customizable, allowing you to turn on lights at different brightness levels.

What Interferes With Motion Detectors?

Motion detectors work efficiently as long as they are correctly installed and frequently maintained. However, there are a few aspects that interfere with their functioning, triggering false alarms. They include

  1. Poorly Designed Motion Sensors

Your security system is more vulnerable to false alarms if you did not consider your home’s requirements during installation. Moreover, members in your home and how you use the facility affect the system’s functionality.

For instance, smoke detectors place near heat sources easily trigger false alarms. Hence, position the gadgets away from fireplaces and stoves. In addition, steam from the bathroom interferes with the functionality of the sensor and increases nuisance alarms.

A home with pets needs a pet-friendly motion detector for optimal safety. Otherwise, a natural sensor causes all kinds of frustrations when pets constantly activate the alarm. Also, loose doors and windows can trigger false alarms when they jiggle.

Fortunately, you can prevent the above scenarios by hiring a professional to install a custom security unit instead of relying on a pre-packaged security product.

  1. Human Error

The person using the motion detector may interfere with its functionality, especially if they are not familiar with the system or are not properly trained. Common culprits include friends and family staying with you, babysitters, and children.

  1. Outdated or Old Security Equipment

Replace your motion detectors if they are old and causing a lot of false alarms. Usually, we have two types of older security equipment that cause nuisance alarms.

  • Non-Supervised Wireless Devices. Nowadays, the security control panel checks the gadget every 24 hours to confirm that everything works well. However, old motion detectors do not communicate with the monitoring team and, worse still, cannot send a signal.
  • Old Ionization Smoke Detectors. This technology is not reliable as photoelectric sensors and is more prone to false alarms. They are common in homes built 12-15 years ago.
  • Outdated Glass-Break Sensors. These gadgets listen for breaking glass sounds. But this leaves them vulnerable to false alarms from other similar sounds like a movie with crashing noises or glass noises in the kitchen.

Contact a reputable home security company to assess your existing home security system to point out any weak points and address them.

  1. Lack of Maintenance and Upkeep

Though security systems do not need much care and maintenance, ensure you do not neglect them altogether. False alarms are often caused by:

  • Dust:  Older smoke sensors mistake dust for smoke and trigger a false alarm. This happens when the home is undergoing construction or remodeling.
  • Dead Batteries: Motion sensors with flat batteries are more likely to activate a false alarm.

So, cover your smoke sensors temporarily when working on dusty projects and replace the batteries as soon as the indicator gives a low-battery alert.

  1. Malfunctioning Smoke Detector

Although this issue is rare for home security systems, consult a professional to evaluate the unit for any malfunctioning. The expert will help find and replace the faulty gadget triggering false alarms.

How Do You Outsmart a Motion Detector?

Outsmarting a motion detector is tricky. However, understanding its designated area and specific room placement can help you get past the unit without setting it off.

In addition, though most motion sensors are very responsive to movement, they rarely detect movement in every place. So, once you know how to fool them, you can avoid waking up people during the night.

Below are simple steps to outsmart a motion detector.

  • Step One

Learn how the sensor works. For instance, most motion detectors have a semicircular view and look for heat waves from moving objects. Thus, they alert the homeowners after being tripped and switch on the siren or light for a certain duration.

  • Step Two

Trip the sensor on purpose until the homeowner switches it off. Furthermore, motion detectors are easy to fool by blowing tree branches and leaves. Also, the intermittent light frustrates most people who simply shut the detector off.

  • Step Three

Reduce the heat amount you are giving off. Remember, some motion detectors search for infrared heat: thus, they’re triggered by a person-sized heat spot. Try soaking in a cold bathtub to reduce the heat on your body. Or train a dog with a lower heat profile to do your bidding.

  • Step Four

Use a masking sound for motion sensors that listen for white noise within the targeted area. This way, your footsteps, and breath will not trigger the alarm as the detector will be busy coping with the white noise.

  • Step Five

Avoid moving when you realize that you need to pass a motion detector. Also, evaluate the area first to understand the environment surrounding the sensor. Then, determine paths that bypass it.

Look for motion detectors around you. Usually, homeowners palace them on ceilings or directly across each other to cover a larger area. Once you see the gadget’s positioning, determine a possible path around its field of vision.

  • Step Six

Move slowly along the walls with motion sensors and as low as possible. Further, many detectors have blind spots, making it difficult to detect motion directly beneath them. But beware of sensors pointing in your direction from the other side of the house.

This strategy also fools older motion detectors. Moreover, it requires some practice, but you can get past the sensor by moving too slowly for it to detect.

  • Step Seven

Crawl through open spaces or in front of big furniture pieces. Generally, motion sensors are pet-friendly and may confuse you for a pet as you move through the room. Since they allow small animals to move freely, you won’t set off the alarm.

  • Step Eight

Block the motion detector with cardboard or a piece of paper. Place the accessory in front of the device slowly and attach it to the gadget before proceeding.

Where Is the Best Place to Put a Motion Detector?

Choosing the best place to put a motion guarantees a wide coverage area regardless of the number of sensors in the facility. Thus, you are sure of maximum security while saving money and time.

Suitable places to position your motion detector include

    • Corners. A corner gives the motion detector the perfect view of the room. Moreover, it delivers a wider view than placing the device on a flat surface or ceiling.
  • High Traffic Areas. Areas, where the flooring gets worn down because of traffic, are ideal for motion sensors. Further, intruders must walk through these spots, exposing themselves to the detectors.
  • Over a Doorway. Keeping motion sensors out of intruders’ sight prevents them from making any malicious moves. They won’t know the gadget is there until the alarm sounds.
  • Basements. Usually, basement doors and windows are prime points for trespassers. So, motion sensors work best as most basements have few barriers and do not heat up like garages. In addition, motion sensors are perfect for flood sensors as they detect moisture on the floor and alert you before too much damage happens.
  • Six to Eight Feet Up.  Placing the motion detector six to eight feet up gives it a bird-eye view while minimizing the blind spots. You can also position it on the ceiling but ensure it has a full 360-degree viewing angle.
  • Behind Your Valuables. Motion detectors protect your valuables as they trigger an alarm when a burglar gets close to them.

Similarly, we have the wrong locations for motion detectors. They lead to blind spots and false triggers.

Below are a few motion sensor locations to avoid.

  • Stairs. Avoid positioning motion detectors at the top of the stairs. Otherwise, pets will easily activate them as they’ll appear bigger to the gadget and set off the alarm.
  • Behind Large Furniture. Placing an infrared motion sensor behind tall furniture that sticks out creates a shadow or blind spot. Therefore, avoid wardrobes and bulky entertainment centers.
  • Garages, Attics, Patios, and Sunrooms. Motion detectors use infrared technology for high-temperature detection. Thus, avoid keeping them in on-climate-controlled areas that heat up. Instead, consider alternative options like glass break, security, window, and door sensors.
  • Across from Doors. While it is good practice to avoid placing motion detectors across doors, it depends on your home’s layout. Also, remember that passive infrared sensors cannot see through walls. Hence, you may limit its detection scope by positioning it directly across the doorway.
  • Near a Heat Source. Motion detectors infrared detect sudden temperature changes. Hence, placing them near a radiator, light fixture, oven, or heating vent increases the area’s temperature, increasing the likelihood of false alarms. Fortunately, most modern windows block sudden temperature changes from the sun. But if you have older windows, avoid keeping the sensors where they can heat up.

How Far Does Motion Detection Work?

Motion sensors work anywhere from 50 to 80 feet. A typical detector will not cover an open workspace or long hallway. Thus, you’ll need several around your home, especially where people frequently walk, such as bedrooms, staircases, hallways, and living rooms.

Moreover, since a motion sensor cannot detect someone walking directly towards it, position it alongside a hallway where a trespasser walks parallel to it.

Make sure your motion detectors are at least ten feet away from radiators, windows, and heating vents. Otherwise, abrupt temperature changes and HVAC-related airflow may activate false alarms.

Frequently Asked Questions

  • How Does a Motion Sensor Work?

Passive infrared motion detectors receive heat signals from items within their proximity. Further, if the intruders move quickly or emit huge energy amounts, the detector completes its desired action. On the other hand, a microwave sensor emits waves and detects reflections from objects.

Both motion detectors have their weaknesses when operating independently. Thus, you need a dual-technology device using features from both sensors to activate the alarms. In addition, using two sensors reduces the frequency of false alarms.

  • Do Motion Sensor Lights Only Work at Night?

Most motion sensor lights only work during the night. They detect motion after dusk and only allow the sensor lights to toggle in darkness. However, you can configure the lights to work all day, depending on your preferences.

Motion detector lights operating in the dark are excellent if you want to consume less electricity. They decide when to toggle the lights on during the night. But again, depending on the sensor lights, you can easily keep them operational during the day.

  • How Do You Disrupt a Motion Sensor?

You have to darken the sensor’s lens to disrupt a motion sensor. This way, it cannot pick up heat signals. Also, identify the sensor’s placement and map out its view. And sneak up to create a blind spot and cover the detector’s lens with paper or cardboard.

However, this strategy does not work well with sensors in high-sensitivity mode. Besides, the sensor may not pick up motion from blind spots. So, try to remain still during your move to keep the sensor from triggering.

  • What Can Set Off a Motion Sensor Light?

Motion sensor lights are set off by moving objects and heat sources, especially if they use passive infrared radiation technology. The most common triggers include rustling leaves, humans, cars, and sunlight.

Ensure outdoor sensor lights cover a choke point without causing false triggers. Mount it inwards on the porch to avoid detecting cars out on the road. Also, with a few tweaks, the gadget can operate through a glass.

  • How Can I Tell If My Motion Sensor Is Bad?

Wire the device and confirm if you can bypass it. However, these electricity checks present a shock hazard, requiring you to be careful. If the lights are faulty, the fixture needs a replacement.

A motion detector can also malfunction when the lens is dirty, defective, or malfunctions due to the electrical circuit. So, use a voltage meter to confirm whether the fixture receives the required power amount.


Without a doubt, motion detectors are the best security options for round-the-clock security. In addition, you do not have to be in the targeted zone to know that there is a guest on your property. The gadgets send alerts to the control panel and your mobile device, allowing you to monitor your home while away.

One intriguing attribute of motion sensors is that they can operate in complete darkness. We have moved on from using age-old fresnel lenses to passive infrared, ultrasonic, and microwave technology. This way, the gadgets can detect motion without light in the surrounding area.

Check out the above article for more insight into motion detectors and how to get the most from them.

Do Motion Detectors Work In the Dark?

Motion detectors work in the dark, thanks to the advanced technology used. For instance, passive infrared motion sensors look for changes in infrared energy whereas microwave ones detect alterations in the emitted waves.

Infrared energy and wave deflection can be detected regardless of the light amount in the controlled area. In addition, the motion sensors do not need to capture images in motion detection. Thus, they work just fine in complete darkness.

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