How to know if its a real mirror, or actually a 2-way mirror

When we visit toilets, bathrooms, hotel rooms, changing rooms, etc.,
how many of you know for sure that the seemingly ordinary mirror hanging on the wall is a real mirror, or actually a 2-way mirror (i.e., others can see you, but you can’t see them)?

… There have been many cases of people installing 2-way mirrors in female changing rooms . It is very difficult to positively identify the surface by looking at it.

So, how do we determine with any amount of certainty what type of mirror we are looking at?

Just conduct this 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 it is GENUINE mirror.

However, if your Fingernail DIRECTLY TOUCHES the image of your nail, Then  BEWARE! IT IS A 2-WAY MIRROR!

Thanks for your attention.