Turn off the lights in the room behind the mirror
Shine a bright flashlight at the mirror from your side
Look for any visible room or movement behind the glass
Tap the mirror and listen for a hollow or solid sound
Check whether the mirror is mounted directly on a wall or has a gap behind it
Place your fingertip on the mirror and see if there is a gap between your finger and its reflection
Compare the reflectivity with a normal mirror
Look for hidden seams, vents, or camera lenses around the frame
Check if the mirror stays unusually clear when the room behind it is dark
Ask for access to the area behind the mirror to verify it is a standard wall-mounted mirror