LOL! I worked for a jewelry store chain that had exploding dye packs hidden in all of the diamond trays. To my knowledge they never foiled a robbery, but every year a couple of them were set off in the stores by employees who were screwing around with them.
Working for the Army, I once saw a nerve agent antidote auto-injector on my boss' desk. Since this was an Army civilian, and the only ones they ever had access to were the training simulators (which look real), I picked it up and fooled around with it. Let's just say it's a good thing I didn't stick it into my leg, but instead had it pointing in a safe direction. Turns out he had it from a deployment, and it was the real deal.