How do hotel mirrors distinguish between double mirrors?

The methods to distinguish the double mirrors in this place include finger test, tapping and listening, brightness comparison, etc.

1, finger test method: put your finger on the mirror, and there is a clear distance between your finger and the reflection in the mirror, then this mirror is an ordinary mirror. Fingers are closely connected with the reflection in the mirror without any distance, so this mirror is a double mirror.

2, tapping listening method: tapping the mirror, the sound is empty, with a slight echo, then this mirror is a double mirror. Because the back of the double mirror is empty, the tapping sound will be fuller.

3, brightness contrast method: stick a small cosmetic mirror next to the big mirror and compare the brightness of the two. If the brightness of a big mirror is obviously lower than that of a small cosmetic mirror, then this big mirror is a double mirror.