Cat's eye in front of the hotel

Cat's eye, also known as door mirror, is a small optical instrument installed on the door of a house. Its function is to let people inside the house observe the situation outside, and at the same time ensure that people outside the house can't see the house clearly. A simple door mirror consists of two lenses, one concave lens is on the outside of the door and the other convex lens is on the inside. The focal length of the concave lens is very short, and the focal length of the convex lens is very long.

Cat's eye prevention introduction:

Cat's eye protection, commonly known as "cat's eye protection observation mirror", is a kind of equipment placed outside the cat's eye, which can clearly observe the indoor situation through the cat's eye. The vast majority of households have installed security doors, but some security doors have some space outside the cat's eye, and there is nothing to cover them. In this case, the cat's eye observation mirror has a chance. The main purpose of "anti-cat's eye" is "peeping".

Cat's eye protection is a kind of peeping tool specially designed for "cat's eye", which can peep at the indoor situation from the outside. With the help of the cat's eye, everything in the room can be seen with the naked eye, and the weight is still very light. The lens barrel is very small and can be completely covered by the palm of your hand. You can put it on your belt, pocket, vest, or buckle it on a key chain.

Based on the opposite principle of cat's eye imaging, the built-in lens sequence is changed to "reverse view". You can directly observe the indoor situation from the cat's eye in the opposite direction outside the door. You can also connect a camera and a monitor to shoot the situation at home. It is usually used by thieves to steal things.