I think lasers are pretty wack when you think about them through this lens. A small, wand-like object in your hand can make light appear from seemingly nowhere. If it’s powerful enough it can set things on fire or blind people. Not to mention larger ones like laser cutters or the LLD, used to destroy missiles midflight. Thats sure to blow some feudal peasant minds
Audio/video technology came to mind for me too. There’s so many layers of technological development to get to even the most basic A/V displays. And even more to have something to play on it. It’s sure to amaze or terrify some people from ages past. Similarly, navigation. Through something like a smart phone, it would probably be baffling to the brightest minds of the early 20th century, let alone centuries ago