Uhh, because of the heat of the raspberry pi & camera behind there
this post was submitted on 24 Sep 2025
345 points (98.3% liked)
Mildly Interesting
23512 readers
720 users here now
This is for strictly mildly interesting material. If it's too interesting, it doesn't belong. If it's not interesting, it doesn't belong.
This is obviously an objective criteria, so the mods are always right. Or maybe mildly right? Ahh.. what do we know?
Just post some stuff and don't spam.
founded 2 years ago
MODERATORS
Ah yes, 10W of heat :3
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?
there are no "one-way" mirrors. You just need to make your side darker than the other side (there's a reason the observation side of a two-way mirror is never brightly lit, but the interrogation room is)
Tldr: put your face right up against it and use your hands to block out as much light as you can
load more comments
(3 replies)
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!
You want there to appear a "space" between your fingertip and the mirror, if touching it directly. If there's no space, then say cheese.
load more comments
(6 replies)
This is ancient advice for two-way mirrors, IIRC nowadays even legit mirrors can reflect directly from the front instead of the back. In this age of spy cameras this is mostly irrelevant.
Another tip was shining a bright light to illuminate the supposedly dark room on the other side, which again, would be way more expensive than a smoke detector spy camera.
load more comments
(1 replies)
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.
load more comments
(1 replies)
load more comments
(1 replies)
Ahh yes, because that would produce exactly square shaped heat.
Why else would it be called the inverse square law?
- Gets rid of fog
- is in shape of a square
Makes sense to me!
load more comments
(3 replies)
Guessing this is a hotel bathroom by the looks of it.
Then it very likely has a mirror with integrated heating. I have one myself and love it.
It’s heated.
There's a ghost in your house that's trying to tell you "rectangle", but it's illiterate.
Try to figure out what "rectangle" means.
Nah, just means that the mirror can't render the Unicode character that the ghost has sent.
It was the poop emoji
or the eggplant emoji. its placed after a shower.
Don't believe any of the other comments, this is clearly a one-way mirror with a camera inside. That conspiracy theory you've been thinking about a lot lately is true, and even worse they know you are on to them. Remember that creak in the floorboards you dismissed as the house settling? Footsteps. The way your coffee mug was turned slightly counterclockwise this morning? Intentional. They watch you when you sleep, and know how much time you spend looking at your phone.
Or it's what the top comment said. Sleep tight!
Or it's what the top comment said. Sleep tight!
Writing this in the top comment doesn't help, like, at all...
There are coatings /sprays for this
I think in this particular case it might be an integrated heating element like this: https://clearmirror.com/products/shower-clearmirror
They're popular in shower rooms in Japan.
You're popular in shower rooms in Japan.
A gee, thanks.
load more comments
(11 replies)
This comments section feels like schizophrenia.
These are such a good idea. It works by having a heater behind the mirror which prevents the condensation.
These are such a good idea. It works by having a heater behind the mirror which prevents the condensation.
load more comments
(1 replies)
For anyone who wants to achieve the same effect take a dry bar of soap and rub some into an area of a mirror in whatever shape you like (circle, square etc). Then buff it out with a dry soft towel or cloth until you can no longer see the soap. Next time you take a shower that part of the mirror won't be fogged up. Reapply soap and buff out every couple weeks or so if you want it to stay that way.
load more comments
(2 replies)
I had this happen in a hotel, and being curious I removed the mirror, and yes there was a hole in the wall behind it, no there wasn't a camera there. It was just were they had ran the wiring for the lights on the mirror.
It would make sense that it serves like an access hatch to a terminal block that feeds the whole room. It's simple, costs nothing, is easy to get to (compared to having it sealed in the wall), protected from splashing and prying guests, and close to where you want most lights and outlets.
being curious I removed the mirror
protected from [...] prying guests,
These are such a good idea. It works by having a mirror behind the heater which prevents the reflection.
Alright, but now the heater is in the way.
Yeah, that's why it prevents the reflection
load more comments
(1 replies)
These are such a good idea. It works by having a heater behind the mirror which prevents the condensation.
Ps. Excuse the multiple posts. fedia.io was having a moment. I’ve deleted them now
Apparently no one here has been to a Home Depot or Lowe's in the last 15 years.
You can achieve a similar effect at home by using your hairdryer on the fogged-up mirror!
load more comments
(11 replies)
Maybe somebody's stashing delicious freshly baked goods back there?
It's a two-way mirror and there's a camera on the other side recording you 24/7.
Isn’t a two-way mirror just a window? I think you meant “one way mirror.”
No. English is just hella stupid. 🤣
A one-way mirror, also called two-way mirror...
How many ways is a normal mirror, then? Do we call it a "no way mirror"?
load more comments
(2 replies)
load more comments
(2 replies)
load more comments
(1 replies)
load more comments
(5 replies)
Just posting to say I was here when everyone replied with "These are such a good idea. It works by having a heater behind the mirror which prevents the condensation."
load more comments
(1 replies)
view more: next ›