[airforce1]

...unless you run afoul of any of their many obscure laws, even unintentionally. I had a relative travel to Japan with his family. He's into locksport (watches Lock Picking Lawyer, etc). He had some lock picking paraphernalia on his person that he forgot about since he just carries it around 24/7 without thinking about it. Long story short, they were discovered in a metal detector at some point and Japanese security whisked him away to an interrogation room. He tried to explain locksport and youtube but the Japanese police were incredulous. He spent a full day in Japanese detention (leaving his wife and kids stranded in Tokyo without him) and at one point it was looking like he might be facing more serious charges, but then luckily someone from an American military base was able to bail him out somehow.

[mvdtnz]

This doesn't seem like an "obscure" law to me. In fact if this is a hobby of yours I would expect you to understand that it's not legal in a number of places.

[airforce1]

It was an honest mistake, especially for someone who rarely travels.

It could happen to anyone in a country where possessing lock picks is not a criminal act. For example, your sibling might get you some picks in credit card form factor one year for Christmas. You put them in your wallet and forget about them. You travel a bit within the USA and nobody cares. Then years later you travel to Japan and are whisked away to jail because of a thing you forgot about in your wallet. The Japanese don't understand why an innocent civilian would ever have such a thing; therefore you must be a nefarious criminal.