A warning system. How curious – not what I expected at all!

Yeah, I debated between that and a weapon and felt like the warning system had the best potential for interesting storytelling. :)

I was also thinking passive weapon, but i like your idea of a warning system a lot. no radio comms needed.

And that is often one of my goals in storytelling — take the expected and turn it into something unexpected. I hate predictable stories. :)