A year or so back my son and his friends built a muon detector as a high school project, and then flew it from London to Germany and back to measure muon rates

A year or so back my son and his friends built a muon detector as a high school project, and then flew it from London to Germany and back to measure muon rates at altitude. Basically two metal boxes glued together, with some hand cut holes for display and power. Inside, a large block of solid plastic scintillator, wrapped in foil, with a bunch of hand-made electronics connected to it. Suspicious? Only a bit. I wrote a letter on headed university paper, explaining what it was, and with contact details in case they needed to phone. At Stansted, the kid carrying it got the third degree, eveything put though the explosives sniffer, and so forth. The security person afterwards told him it ticked all the boxes except one for a bomb. Would love to know what that one was! They did eventually allow it on the plane though, and got really good data from the flight. On the return flight, security at Cologne didn't look twice - just went straight through the x-ray machine, didn't even get pulled aside. Must have been asleep on the job.