Airport security: what if I carry an item with traces of explosive?

A friend was travelling from New Zealand to London. He got the check - swabbed his bag for explosives/gunpowder. He's totally innocent so isn't worried - until he came back positive.

Immediately, security was alerted and he was taken for secondary screening. They separate you from your bags, and he was interrogated for a while. It quickly became evident he knew nothing, and the bags were searched and nothing was found, so he was released and allowed to board his flight.

So that's it - an extra check, some questions, the point is to spot possible explosives and then eliminate false positives.

And why was his bag flagged? He was mystified until a few days later when talking to his father on the phone, who laughed and remembered he'd recently been cleaning his shotgun at home ... over the very bag his son took to London ;)

I also have a ring from a hand grenade as a keyring. I have travelled to the US and Europe many times and this has never been an issue. I've never even thought about it.

I've also travelled just a few hours after handling (but not firing) other ammunition, mostly 5.56. I've never had a problem with explosives being detected.

You should know that all my handling of ammunition has occurred in Israel, where we are famously careful about letting dangerous contraband get through. If any nation would have given me a hard time, it would have been us!

This is a not-quite-daily occurrence at security gates everywhere. The equipment is now so sensitive you could conceivably get a hit if you hung your coat up beside a demolition engineer's. Or bought certain types of garden fertilizer the morning of your flight.

It's legitimate grounds for a more thorough baggage search and possibly a pat-down. If they don't find anything, no problem.

However, it would be a rather bad time to carry 4kg of marzipan in plain foil wrap. marzipan isn't illegal either, but it will take a LOT longer to determine that fact. Put an old-fashioned alarm clock (wind-up type) in the bag for extra entertainment.

Some people trigger radiation alarms if they have had a PET scan recently - they are emitting just enough radiation to trigger the alarms. Why so sensitive? A well-shielded bomb emits about the same trace amounts. Couple of questions, quick bag check, have a nice day.

Have had swaps come up positive for "explosives" all the time when flying with photographic film.
It contains celluloid base and silver based compounds, which happen to also be a part of several explosives...
Nothing happens, they just do a hand search of your bag. I seriously doubt they'd even recognise your keyring for what it is, unless they've themselves been in the armed forces and worked with the same type of grenade you used, and that recently enough to not have forgotten such a minor detail.
And no, after months or years in your pocket there's no residue left on it at all. Maybe for a few days, not for years.

I have traveled with expended cartridges (only the brass left after firing) since I used it as a signature in Geocaches I found. I took it through security several times until one day the security in Czech Republic noticed it and asked me about it. I explained why I had it and they said "Ok, but I unfortunately have to confiscate these". Not a problem for me, I can get many more from the shooting range I'm an instructor at. I just handed them over and was on my merry way, no additional bag screening beyond showing them the suspected item.

My father who also works at the same range as me have traveled several times with live ammunition in his carry-on by mistake. A couple of rounds had fallen out in his bag and lay hidden in the bottom which he noticed much later. I wonder what might have happened if they discovered THAT.

Another time I got swabbed when recently having been at the shooting range and firing weapons (day before or something) and was using the same jacket and shirt. I was swabbed both when entering the security check and when exiting (random selection yeah... More like swab the guy with a rifle print on his club shirt). it turned up negative both times though.

Bottom line, no, no issue with your pin, at all.

Working in this industry, I can tell you that there are many false positives. In some cases, there are limitations due to technology: chocolate can be confused with explosives under certain circumstances and anything "high Z" (very dense) is grounds for suspicion. In other cases, recognition algorithms are far from perfect but all we've got (the controversy over terahertz imaging has resulted in "Gumby outlines" for body scans with suspicious elements highlighted by ... yep, those very same insufficient recognition algorithms). Tolerance on the part of the inspectors is certainly to be appreciated as is your diligence. Safe travels!