Have you seen recently advertise on television or see any hoarding for Two way glasses/mirrors? If you seen or even heard about two way mirror then you should aware of its side effects.
May be Hotels, shopping Malls, showrooms can cheat you by using two way glasses.
So for that awareness i have a trick for you so you can easily detect it is a two way mirror or not.
When we visit toilets, bathrooms, hotel rooms, changing rooms, etc. How can we sure that the seemingly ordinary mirror hanging on the wall is a real mirror, or actually a two way mirror? i.e. they can see you, but you can't see them. There have been many cases of people installing 2-way mirrors in female changing rooms or bathrooms or bedrooms.
Conduct the simple test:
Place the tip of your fingernail against the reflective surface and if there is a gap between your fingernail and the image of the nail, then its a genuine mirror.
However if your fingernail directly touches the images of your nail then beware its a 2-way mirror (There may be someone seeing you from other side).
So remember every time when you see mirror do this fingernail test.
The reason there is a gap in real mirror, is because the silver is on the back of the mirror under the glass.
Whereas in a 2-way mirror silver is on surface of the glass.
So keep in mind every time you visit any hotel, showroom, shopping mall check the mirror with fingernail test.