Ok, that was kind of what I was thinking. I know in movies and TV shows they usually are "thought of" as inert or duds, and then it always turns out they weren't. But that also always sort if implied they must have been less likely to trigger, if there was reason for the characters in the show to believe they were inert until finding out otherwise.

Buy yeah, in reality it always seemed to me like they must get more sensitive over time. The only way I could have maybe seen them get "safer" is if rust rendered all the contact pins immobile or something. But even if that could be the case, it still wouldn't actually be safer, but could explain why people might initially think it was if they didn't know.