I drop my helmet at least once a week. I check it over frequently for cracks. Earlier this year I managed to drop it just right on a sidewalk so that the back side hit the ground on a point. The helmet developed a crack and I was able to pull that section of the helmet apart without too much effort, so I retired that helmet.

I'm quite good at dropping things. My stainless steel water bottles carry an impressive collection of dents. I tend to analyze items for durability before purchase for this reason.