TikTok is full of people discovering spy mirrors in their hotel rooms and Airbnbs.
(Phewthis ones fine!
Unfortunately, these videos rely on a misunderstanding of how mirrors work.
(It doesnt involve your fingernail.)
What is a spy mirror, anyway?
The TikToks all say they will show you a way to find out whether youre being watched.
People on the other side can see right in.
These mirrors do exist.
Im going to call them spy mirrors to avoid confusion.
Now, do spy mirrors existin hotels?
But you never know.
So why not just use your finger?
Good news: people simply putting their fingers against mirrors are all over TikTok, as well.
The most common style of mirror youll see in home and hotel bathrooms is made of glass.
This way, when you put your fingernail against the glass, youre not directly touching the reflective part.
This is called a back silvered or second surface mirror.
So, yes: normally youll be able to see a gap.
The gap just tells you that the mirror is back-silvered.
Real mirrors can be back-silveredorfront-silvered and still be legit, normal mirrors.
What youre looking for, if youve got your eye out for spy mirrors, is something that ishalf-silvered.
That refers to the jot down of coating, not just where its applied.
But it could also be a front-silvered regular mirror.
(These arent very common, but they exist.)
The makeup mirror just has thinner glass than the others.
Mirrored sunglasses and spy mirrors work the same way.
Three things make up the effect:
Light from the front can pass to the back.
Light from the back can pass to the front.
The whole effect depends onlighting.
Its like a more dramatic version of how your homes windows appear at night.
You cant see outdoors because the reflections from indoor lights are brighter than whatever is shining in from outside.
The half-silvering just enhances this effect.
How to actually spot a spy mirror
Forget the fingernail test.
Put a flashlight right up to the mirror, and shine it through.
Thats all there is to it.
With the flashlight trick, it’s possible for you to literally see right through them.
A mirror on a wall that is shared with an employees only room?
Yeah, Id be suspicious.
Somebody like putthaton TikTok instead of yet another look at my fingernail video.)
But Ive seen at least one TikTok where the supposed spy mirror looks like a shower door.
(Heres apublic bathroom that uses the same trick.)
Otherwise, you just see your reflection.
And finally, polished metal can be reflective and would not show a gap.
Thats not a spy mirror either.
