Women, pay special attention to this one.
We´ve all been in fitting rooms when we´re changing clothes, right? How do you know if it is a 2-way mirror(people watching you from the other side)?
There is one test to know for sure! And I do this test everywhere I go including hostels and hotels.
Stick you thumb nail to the mirror.
IF YOU SEE YOUR THUMB NAIL TOUCHING THE THUMB NAIL REFLECTION WITH NO SPACE IN BETWEEN, YOU COULD BE ON CANDID CAMERA 
!
On a normal mirror, stick your thumb nail to the mirror and you will see a space between your actual nail and it´s reflection.
For FYI
Linear Mode
