How Do Motion Sensors Work In the Dark? Let’s Find Out

Motion sensors are one of the best security gadgets for round the clock security. One intriguing aspect of these devices has always been their operation in the dark. Luckily – they’ve moved on from using age-old fresnel lenses – but how do motion sensors work in the dark today? Let’s find out!

How do Motion Sensors Work in the Dark?

PIR motion sensors work in the dark by detecting infrared radiations to pick changes in heat across their field of view. If a heat-emitting object enters the field of view, the motion sensor works by triggering an alarm. Since they don’t rely on light sources, they can work in complete darkness as well.

Ultrasonic radiation-based or microwave-based sensors work by emitting waves and receiving reflections from moving objects. If an object were to move in the field of view of this type of sensor, it would pick up reflections of waves as well.

If you’re intrigued by older motion sensor models, they used fresnel lenses to scatter light and trigger a resistance-based sensor behind it. Moving objects would cause a fast change in the scattered light on the lens and in resistance on the sensor – ultimately triggering it. It’s a bit technical – but hey, it’s a wonder these devices aren’t in common use today. 

Do All Types of Motion Sensors Work in the Dark?

Modern motion sensor models can work well in complete darkness. PIR, microwave, ultrasonic, or dual-tech motion sensors all rely on emission of waves and reception of heat/reflections from moving objects in their field of view. Though motion sensors can cause false triggers in the dark, as well.

Let’s take a close look at the major types of motion sensors in a little more detail.

Passive Infrared Sensors

Passive Infrared sensors work in the dark by detecting infrared radiations only. If the emitters work on low sensitivity or the mode is disabled, the sensor wouldn’t detect anything in the dark. Make sure to test your sensor on installation in the dark to see if it works well or not. 

A caveat around PIR sensors would be their inability to work through a glass. Since IR rays aren’t able to pass through a glass, the sensor wouldn’t pick up changes in heat outside the glass. It’s better to aid the motion sensor with a glass-tampering device rather than placing the sensor outside.

Ultrasonic and Microwave Sensors

Ultrasonic or microwave-based sensors emit waves and await reflections off of objects. These sensors are easier to fool since they pick up changes in movement in their proximity. If an object is stable and the reflections aren’t suspicious, the sensor might never trigger.

Either way, these motion sensors don’t rely on light to work in the dark. It’s why even these motion sensors can work well for you in the dark.

However, you should be wary of false positives in a microwave sensor which might pick up reflections from any object in its proximity if the sensitivity is high. It’s why these devices don’t exist independently and are complemented with a PIR sensor.

Dual-technology Sensors

Dual-technology sensors are perhaps the safest options in terms of working in dark and a low false alarm rate. They combine features from both types of motion sensors – PIR and microwave. For the alarm to trigger in the dark, an object has to move and emit some form of heat to trigger.

Though these motion sensors won’t work in the dark through a glass either. Since the PIR sensor won’t ever trigger even though the microwave sensor would.

Complementing your motion sensors with other security gadgets is perhaps the safest option.

FAQs on Motion Sensors Working in the Dark

It’s time to answer some questions! We’ve picked up some questions asked by fellows concerned about their home security on the topic. Let’s get to answering them now:

How do motion sensor lights work in the dark?

Motion sensor lights work in the dark by detecting infrared radiations and looking for changes in energy. If a heat-emitting object enters the proximity of the motion sensor, the lights toggle. If your motion sensor light uses microwaves, it will only toggle when an object reflects the waves.
Almost every human being emits some form of infrared energy. Only a portion of the radiation frequency spectrum is visible to us, whereas radiations above or below this spectrum e.g. infrared radiations aren’t visible to us. They’re heat maps across which changes are fairly easy to notice by these sensors, even in the dark. 

How does a motion sensor work?

PIR-based motion sensors pick up heat signals from objects in their proximity. If an object moves quickly or emits a huge amount of energy, the sensor completes its desired action. An active motion sensor, such as a microwave sensor, emits waves and detects reflections off of objects.
Both types of sensors have their flaws when they’re operating independently.
A dual-technology motion sensor uses features from both types of sensors to trigger alarms. Using the best of the two, the frequency of false alarms is much lower. 

Do motion sensor lights only work at night?

By default, most motion sensor lights only work at night. They begin detecting motion after dusk and only cause the sensor lights to toggle at night. If you’d like the motion sensor lights to work all day, the lights can be easily configured to do so.
Motion sensor lights which operate in the dark are great if you’d like to save a few bucks from your electric bill. Let the sensor decide when to toggle the lights on at night. Again, depending on your sensor lights, you can easily keep them running all day by changing these settings.

Let’s conclude our piece on ‘how do motion sensors work in the dark’.

Our recommendation would be to pick a dual-technology motion sensor if you’re yet to buy one. With the best features of the two types of motion sensors, you won’t regret this purchase.

Are you ready to secure your home today?