Ignoring part of the scene

Switch to "Ignore" and draw over anything that causes trouble: a television, a window onto a street, a clock with a moving hand.

You can have as many of each as you like. A region is a list of shapes, each marked Watch or Ignore, and movement counts when it falls inside any watched shape and inside no ignored one. Watching a doorway and a window while ignoring a television and a wall clock is four shapes, and that's a perfectly ordinary setup. The sidebar keeps a tally so you can see what you've built.

Exclusions take precedence wherever they overlap, and one ignored area can cut across several watched ones. You can also draw an ignored area with no watched area at all, which reads as "watch everything except this".

If exclusions end up covering everything you're watching, a warning appears — otherwise the detector could never fire and nothing would tell you why.