Z-wave and mirrors

I was having the hardest time getting my hub to talk to a dimmer switch in my bedroom which is only 25 feet away, and I think I figured out the problem.

First, some communication was happening, because the switches (I tried three of them) were recognized after a few attempts to add them to the network. But after that, they became unreachable.

So I bought an Aeon Range Extender ($20) and placed it almost precisely halfway between the hub and the switch, in the only available location (the house was built in 1969, but it still doesn’t have that many outlets).

The hub could see the repeater fine, but still could not talk to the switch. I started experimenting with various repeater locations with an extension cord, and found that other locations worked—but none that was feasible for a permanent installation. I tried other plugs at various locations but they were all too far or poorly placed.

Finally I tried one plug next to the bed which I had not considered because it is further away from the hub than the switch is. This one worked!

So then I realized that all shorter but non-working paths were going through a large mirror which covers an entire wall about 5 feet in front of the switch (about 5 feet wide and 8 feet tall). Is it well known that mirrors block the 900MHz signal? I had no idea.


I guess it’s depending on the back coating of your mirror. I wouldn’t think the glass itself is the issue. Thanks for posting. This will or could help others later.


Given its a 50yo house, is the mirror also that old? maybe it has paint with lead in the back? lol… This is a really interesting find…


When wireless signal goes through walls, it actually vibrates the wall and some of the energy is changed to heat. My house was built in 1949 and I have two layers of plaster on my walls. One was a plaster board, like today’s drywall, and on top of that was plaster and metal lath. I had a heck of a time with range inside my house. It might have been that the mirror was the straw that broke the camel’s back, so to speak.

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This would not surprise me. The reflective surface is made up of various metals, such as aluminum or mercury, so it could definitely affect the signal.


Mirrors do block signal.

A mirror isn’t just glass: it’s glass coated with metal (literally), and sometimes backed by metal as well. So it’s basically a big metal plate. It will both block signal and reflect (scatter) signal from the front side. :last_quarter_moon_with_face: :first_quarter_moon_with_face:

People who are extremely concerned about EMF frequency pollution, for example, will put mirrored window film on the windows. It will cut signal by over half.

Here’s a video where a guy shows just how much the signal drops with a single piece of film.

If it’s a regular wall mirror and it happens to also be backed with metal, you get even more blockage.

So as always “all home automation is local.” Most people in this forum have already heard my story about the frying pan in the kitchen, but this is the same thing. :sunglasses:


Could you give a quick reply for those of us who haven’t? :wink:

Engineering class exam from college. A house is set up for home automation and everything works great. Then the family moves in and things start breaking all over. :scream: The exam consisted of before and after pictures, and we had to note everything that might be causing problems or blocking the signal.

The one that everybody, including me, got wrong was in the kitchen. The family had some cast-iron pans. When one person did the dishes, the pan got put on the lower right side of the cabinet. When someone else in the family did them, the pan got put on the upper left. In one of these two positions, signal into the kitchen (always tricky because of the appliances) got blocked.