Your friend gets pinged
If you screenshot a boop or another protected screen, the other person's phone gets a heads-up within a second or two. Screenshotting isn't invisible here. It's social. Whoever shared something knows it was captured.
Most screenshots come back black
Protected screens also blank their own contents at the moment of capture, on both iOS and Android. So a lot of screenshot attempts save a plain black image instead of the photo, because the protection runs before anything reaches the camera roll.
It runs without reading your messages
Plenty of apps do screenshot alerts. The difference on boopr is that we don't have to read your content to do it. Detection happens on the device, on top of the same encryption that keeps us from seeing your stuff in the first place.
What's protected
Boops and other sensitive screens are covered. The protection is strongest exactly where it matters most: the disappearing, sent-to-specific-friends content.
It's a strong deterrent, not a force field. Someone can always point a second phone at their screen and photograph it, and no app on earth can stop that. What boopr does is make casual screenshotting both visible (your friend gets pinged) and mostly useless (the capture comes back black). Share accordingly.