Plains Of The Altiplano, Bolivia, Spanish Salar De Uyuni Mirror

A two-way mirror is a sheet of glass coated with a layer of metal only a few dozen atoms thick, which reflects some percentage of the light incident on it and transmits the remainder to the other side.
• One-way mirrors
One-way mirrors work by overwhelming dim transmitted light with bright reflected light. A true one-way mirror that actually allows light to be transmitted in one direction only without requiring external energy is not possible as it violates the second law of thermodynamics: if one placed a cold object on the transmitting side and a hot one on the blocked side, radiant energy would be transferred from the cold to the hot object.