Does Philips Hue’s Motion Sensor Work Through Glass & Windows?

Infrared vision is the stuff of science fiction and spy movies. Being able to see heat signatures allows action movie heroes to see through walls, but why can’t my Philips Hue Motion Sensor see through a glass window?

Passive infrared sensors work wonders in low-light conditions, but they have their drawbacks. These sensors are far and away the most common type of motion sensor in today’s smart home tech. This guide will prepare you to tackle your infrared sensor conundrums just like the hero in a spy movie. Let’s answer the question: can PIR sensors see through glass?

Not really. Glass disperses the wavelength of light that infrared sensors use to detect motion. The good news is that this is a fairly common concern and there are plenty of solutions to help you work around the issue.

What is the Hue Motion Sensor?

My Philips Hue motion sensor on carpet
My Philips Hue motion sensor.

The Philips Hue Motion Sensor is small, powerful, and affordable. Its utility and design make it the go-to choice for indoor sensors.

This sensor uses a passive infrared system to detect motion. We’ll get into the details of how this works and why it has such a hard time seeing through glass in just a minute.

These small sensors readily integrate into a variety of smart home ecosystems, and they can help you automate your tech.

If you’ve been struggling with a Hue Motion Sensor that is being blocked by glass, let’s take a look at what’s causing this problem and how you can fix it.

Why These Motions Sensors Can’t See Through Glass

Glass is clear, right, so sensors that detect light should be able to see right through it? Well, as the old saying goes, seeing is believing, but it’s not always telling you the whole truth.

Let’s geek out for a moment with some light science. The light that we see reflecting off of everything from paintings to the screen you’re reading this on is known as “visible light.” There are more kinds of light, known as wavelengths, including infrared.

You’ve probably seen colorized infrared footage showing the heat that people and objects give off:

Infrared light signatures from a house
Infrared light signatures from a house

This heat is actually light, just a type of light that people can’t normally see.

Infrared is a powerful technology that can see in otherwise total darkness, but it can’t see through glass.

Infrared radiation is blocked by glass. This is especially true of modern windows which are designed to insulate and prevent heat from passing through. Infrared is also blocked by walls, so it’s not quite what you see in the movies.

In short, glass is just too good at insulation for passive infrared sensors to be able to see through.

So why would anyone want this kind of sensor? Why not just have a pixel sensor that can always see through glass?

Infrared might be stopped by modern glass, but it can see in the dark. It’s easy to turn out the lights and make normal vision more difficult, but much harder to block the heat our bodies are always giving off. This makes infrared ideal for safety and security sensors.

Picking the right sensor is about managing your needs with what the technology is capable of. Let’s dig into how we can make a PIR sensor work for you.

Why Would You Want to See Through Glass

A Hue motion sensor pointed at a window/glass
A Hue motion sensor pointed at a window/glass

Seeing through glass is an interesting problem to have and there are some good reasons to have it.

Security is the most common issue when it comes to PIR sensors being blocked by glass. If your infrared motion sensor is aimed out a window and into your yard, you’re going to need to rely on its ability to see a possible intruder coming.

Glass can also pose problems for smart lights that use PIR sensors at night, but rely on pixel sensors during the day. No matter what angle we tackle this problem from, we’re going to want to come up with some ways for our sensors to see through glass.

Working Around the Problem

This is a problem that we can’t fix directly. In most cases, you can’t remove the window in question, and you probably wouldn’t want to. We also can’t upgrade our PIR sensors. This means we have to work around the issue.

Today, we’re working smarter, not harder.

Try Out a Different Philips Hue Sensor

The Hue Outdoor Motion was designed to help us get around this problem.

This sensor is a PIR that directly integrates with your Hue ecosystem. It also features a built-in dusk-to-dawn detection system that gives you more accurate timing for automatic lighting systems. You can mount this sensor outdoors and bypass the window problem entirely.

While this is probably the go-to solution for most cases, there are some reasons to try another solution.

The Hue Outdoor Motion sensor requires outdoor mounting. If you’re renting, or you just don’t feel like mounting another device on your home, this solution might not be the one for you. These motion sensors are at their best when mounted high up on your home. If heights are an issue, you’re going to need to try another solution on this list.

This sensor might also not be the most convenient option. Let’s check out a few others.

Location, Location, Location

Smart home tech costs money and buying a new sensor just to get around a piece of glass isn’t always that appealing. Thankfully, you might be able to just move things around.

This one is going to depend on the layout and construction of your home. Older glass windows are less heat efficient. This is bad for your energy bill, but great for PIR sensors as they have an easier time “seeing” through single pane windows. If you’ve got a room you haven’t remodeled, or you’re living in an older apartment, you might be able to get away with aiming your sensor out an older window pane.

You can also aim your sensor around the problem. Enclosed porches, different angles, and new setups can all help you get your smart home system working the way you want it to. It’s all about playing around with your current equipment and finding the way you can make it work best for your needs.

If all else fails, you can ditch PIR all together.

Switching to Pixel Motion Detection

There is one major alternative to PIR and that’s pixel-based motion sensors. These have their own trade-offs, but can help you tackle the window problem.

In a pixel motion sensor, the camera or light uses changes in pixels to interpret motion. Software inside the camera calculates the percentage change in color from one pixel to another. Enough change means that something could be moving in the sensor’s field of view.

In many of these systems, you can set the percentage change required to trip the light or camera. This means they can be as sensitive as you need.

Best of all, they can see right through glass! These sensors use the same visible light as you and I do to see. This means they can see straight through glass like Superman. However, just like our caped hero, they have a few weaknesses.

An example of this is the Ring Indoor Camera which is plugged in, and hence uses pixel-based motion detection in the daytime. You can therefore point a Ring Indoor Camera outside your window, and this can detect motion. At this point, you can use an Alexa routine to turn on a light when motion is detected. To do this:

  • Launch the Alexa app and go to the routines section.
  • Press the “+” icon to add a new routine.
  • Enter the name, and then select the “Trigger” section.
  • Here, you want your trigger to be “Smart Home”, and then select your Ring Indoor Cam, before selecting “Motion”. This means that the routine will start when your Ring camera sees motion.
  • Then select “Action” and again choose “Smart Home”, before selecting a smart light. You can then choose for it to come on (or change color or brightness) as you require.
  • Click save, and this routine will work automatically – using a smart camera’s motion detection to turn lights on and off.
  • There is one big downside to this approach, though…

PIR sensors don’t mind if it gets dark outside and that’s because they aren’t looking at visible light. A pixel-based motion sensor needs visible light to see. That means if it gets too dark for the sensor, it won’t be able to see any motion. These sensors can also experience performance issues in heavy fog and can even be held back by glare from our dreaded nemesis, glass.

It’s not nearly as bad as a PIR sensor which is stopped entirely by glass, but bad enough glare can significantly reduce a pixel-based sensor’s abilities.

If none of these solutions have worked so far, it’s time to try something new.

Bring in Some New Technology to Your Smart Home

Your smart home technology might present you with these kinds of challenges now and then, but these are opportunities to explore new tech and new solutions.

One of the joys of working with smart home technology is finding just how adaptable these devices are. If you can create a DIY smart kitchen that prepares a simple breakfast for you each morning, you can work around sensor issues.

The first step on this path is to consider why you want a motion sensor in the first place. If it’s just to turn on an exterior light, let’s say a floodlight in your backyard for safety, you could always try installing a Ring Floodlight Camera or a Nest Floodlight Camera. Even an old-fashioned floodlight plugged into a basic motion sensor can get this job done.

Ring Floodlight Cam wall mounted - bottom view
My wall mounted Ring Floodlight Cam.

If it’s the “smart” part of the tech that you want to maximize, you can try the smart options mentioned above. Both can work with Alexa or HomeKit, though you might need a bridge or a hub to make it work.

The best part about smart home technology is building a system that helps you achieve your goals and responds to your needs. When these kinds of small problems arise, it’s a chance to flex your smart muscles and try something new.

About Tristan Perry

Tristan Perry is a software developer who is passionate about tech gadgets, DIY and housing. He has therefore loved seeing smart homes hit the mainstream. Tristan also has an academic background (in Math & Computer Science), and so he enjoys digging into the technical ways that smart home devices work.

Tristan owns close to a dozen Amazon Echo devices, way too many Philips Hue bulbs and lightstrips, a boat-load of Ring Cameras and Doorbells... and a bunch of other smart home devices too (from Reolink, Google Nest, GLEDOPTO and others).

If you have any questions, feedback or suggestions about this article, please leave a comment below. Please note that all comments go into a moderation queue (to prevent blog spam). Your comment will be manually reviewed and approved by Tristan in less than a week. Thanks!

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