The three separate jobs an intrusion system actually has to do — and why a sensor tripping is nowhere near the end of the story.
Ask most people what an intrusion detection system does and they'll say "it detects intruders." That's true as far as it goes, but it collapses three genuinely distinct functions into one word. A door contact opening or a motion sensor tripping is detection— and detection alone can't tell you whether what just happened was a burglar, a cat, a gust of wind, or an employee who forgot to badge in correctly. Getting from a raw sensor trip to an appropriately-sized human response requires two more steps that detection hardware, by itself, cannot perform.