Smart switch motion detector problem

I got a Smart Home Motion Detector switch and installed it. It seems to work fine, until a glass door in front of it stops it detecting motion. Is this typical of all motion detectors. I thought it would work through glass. I even tried max sensitivity but nothing works. ???

It’s my understanding that PIR motion sensors work by detecting heat and will not reliably work through glass.


PIR (passive infrared) Sensors do not detect human movement through glass, regardless of the brand. It’s just the wrong technology for that.

I’m not sure what brand you’re talking about, but if it’s a PIR sensor, it will not detect people through glass.

In home automation the alternative is usually one of the video processing sensor systems, Typically as part of a security camera. But you have to check each model individually to make sure that it can give you the kind of detection that you want.


hack a “barking dog alarm” that works through doors. I don’t know what the medium is, but I don’t want to stand in front of it.

That’s using a radar sensor. They are a newer type, but have turned out to be not quite as general purpose as the PIR, which is why you don’t see more of them. They can detect somewhat through walls which is both good and bad.

One of the reasons that security systems often deploy PIR sensors is that they view a “room” the same way a human does. That is, the fact that they do not detect through a wall makes the notifications from the system very useful. Someone walking around in an upstairs bedroom will not trigger a PIR sensor which is downstairs in the living room.

Because the radar sensors can detect through a wall, they are more like a guard dog. Anything they “hear“ in 360° will trigger the sensor. That can make it hard to create useful notifications. It also means it’s really easy For an animal or person passing by outside the home to set off a radar sensor. (Or for that matter a squirrel on the roof if the sensor is upstairs.)

So they are good for some purposes, but not for others. They’re pretty much useless for turning lights on when someone enters a room, because they will pick up motion in all the surrounding rooms as well. Also, they typically aren’t good for a security system where the homeowner is home as a family moving around will keep triggering them. People use them mostly for when they are going to be away from home and they want that “guard dog” kind of effect when anyone gets near the house.

Also, some kinds of glass will diffract the signal and it won’t be detected. So you do have to test that as well.

The following is a good look at radar sensors.

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