this post was submitted on 24 Sep 2025
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Mildly Interesting
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Uhh, because of the heat of the raspberry pi & camera behind there
Suppose you were in this situation and suspected something. I’d imagine the space behind it would be totally dark, so what would be a safe way to check if there’s a gap in between without breaking the glass?
I read a long time ago that putting something flat against the mirror will show you. I think if the mirror is legit you’ll see the reflection directly on the surface, if it’s two way the reflection will look like it’s inside the glass.
But I’ve never had the chance to actually test that, so take it with a grain of salt.
Edit: Turns out this is incorrect; thanks to everyone for educating me!
It would be the other way around, if at all.
"First-surface" mirrors where the reflective layer is on the front of the glass are quite fragile, so wouldn't typically used for residential applications (you'd remove the reflective coating by cleaning it).
A regular mirror has the reflective surface on the back of the glass (which is then is further coated with a protective paint), leading to the effect you describe.
I don't however know enough to say one way or the other whether a surveillance mirror would becessarily be a first-surface mirror.
Just checked my bathroom mirror and it looks to be a first-surface mirror