Techsy: Start an 8 planet start and send 80 mk1 scouts onto an enemy planet. It'll put it, and the nearby planets, on alert. It has nothing to do with combat/noncombat, but ship class by size.
Frankly, a spirecraft scout probably should put an AI planet on alert. It's pretty unnerving that you know there's a cloaked ship, and you know it's big enough to be a spirecraft, but you're not entirely certain if it's a penetrator or a scout. That and spirecraft scouts are extremely easy to get ahold of, unlike mk4 scouts/scout starships, and as such should probably have some pretty significant drawbacks.