Uhh, because of the heat of the raspberry pi & camera behind there

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.

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!

There are coatings /sprays for this

This comments section feels like schizophrenia.

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.

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.

These are such a good idea. It works by having a mirror behind the heater which prevents the reflection.

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

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.

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."