In movies you sometimes see someone being interrogated by an officer. When this happens, you mostly see another officer looking at them through what I call a "See-Through Mirror", a mirror that is only mirrored on one side, but you can look through the other side. So in the film, the person being interrogated only sees a mirror, while on the other side of the mirror, someone can watch him/her.
I always found that a scary idea, and I believe most people would agree with me because you know you're being watched, but you can't see by who. You can't see if it is one person, or more. You can't see what they look like, but you know they're there, watching you. Maybe it even pleases them, seeing you. What if they like it?
At the same time, you never hear a sound coming from the other side of the mirror in those interrogation scenes. That's because they try to be completely quiet. But don't you think sometimes those people might accidentally make a sound? Of course they do, but those rooms are almost fully soundproof, so you don't hear it.
Also, I never understood how see-through mirrors work. But recently, I thought of something. When it's night, and you still have your lights on, you can't see what's going on outside, because it's dark. But when it's night, and you walk past someone's house when the lights are still on, you can clearly see the inside of those houses, because it's light in there.
So, at night, your windows are see-through-mirrors. And you can't know if someone is watching you.
But in those movies, the walls are soundproof. In your house, they aren't.
Have you ever heard a strange sound at night, but you didn't know where it came from?