What is a Curtain Motion Detector?
A curtain motion detector functions like a traditional motion detector except that it's detection pattern is much thinner.
Every motion detector has a monitoring "pattern". This pattern is essentially the size and shape of a motion detector's range. Standard motion detectors are built with a broad detection range that can monitor an entire room. A curtain motion detector has a more defined, curtain-shaped pattern that is great for monitoring narrower areas, like human traffic through a doorway (i.e. a store front entrance).