Perhaps it's escaped your attention, but typically the kind of people who are in charge of security at these places have far greater powers than simply asking you a few questions. Depending on how serious they think the threat is, you are potentially going to be held at gunpoint, strip-searched, and allowed to watch as they pull apart any of your luggage they think contains anything they don't like, as well as being arbitrarily delayed, potentially reported in the media, etc. And the best part is, they usually have little accountability for their actions, while you are typically not entitled to any compensation even if they cause your entire holiday to fall apart or cause expensive damage to your property. It's basically subject to their professional (or otherwise) judgement. Now, do you think installing a warning system liable to significant numbers of false positives is going to make this situation better or worse? And if you think any of the specific possibilities I have mentioned here is only hypothetical, please be very clear about which of those powers you do not think the security people have at most Western transport hubs, and I'm sure someone here can enlighten you.