mén / shàng / zhuāng / le / māo / yǎn / ， / bú / yòng / kāi / mén / jiù / néng / kàn / dào / wài / miàn / de / rén / 。

门上装了猫眼，不用开门就能看到外面的人。

There is a peephole on the door, so you can see who is outside without opening it.