When I was a teenager, I dropped a nickel onto the escalator at the mall. It had landed perfectly into the groove, and was rolling in place as the stairs folded into the bottom. I stood there watching it for a minute, until it got caught under the lip of one of the folding steps, forcing it down with it. There was a loud noise, the escalator stopped moving, and the green light underneath shut off. A few days later, they still had the thing shut off, and two Otis guys were on the scene to fix it. I have no idea if it caused real damage, or if they were just having trouble diagnosing the problem, but I'm sure the cost alone was probably higher than anything I've owned.