The "Bomb Clock"

I was given this clock as a token by the group I taught in Belfast, Northern Ireland, many years ago. (Thanks, Albert! You guys were great.)
I was on my way to Sweden and put it in my suitcase without a battery. Coming home a week later and going through security in Stockholm, I was asked if I had anything electronic in my luggage. I had forgotten about the clock and said no.
I was at the gate when I heard my name called and was asked to speak with a man in a dark suit. He asked me if I had anything electronic in my suitcase, to which I again said no. He had a pad of paper and a pen, on which he drew a rough circle as he asked "Anything cyclic?" I realized I had the clock in my bag and told him so.
"Where did you get the clock?"
"I got it from friends."
"Where are your friends?"
I thought he'd freak out if I said Northern Ireland, since this was still when they ad "The Troubles", although they were winding down.
I replied, "Ireland".
He leaned forward, arms out and raised his voice, saying "Ireland!"
I was right, he did freak out. This did not seem to be going well.
"Look, here's the story. I'm a karate instructor and I taught a class there. They gave me the clock as a gift of appreciation. You can tear my luggage apart, if you want."
He looked at me, then said, "I believe you." And he let me go.
When I told the story, people surmised the Swedes thought it could be a bomb, and hence the name for the clock became the "Bomb Clock". It hangs in my home office.