Charger
When you need to charge your laptop, phone, or any other device, you probably see the thick piece of plastic that is at the end of the charger. The part that plugs into your device is built that way so that any interference from another device is blocked and it can do its job.
All these little things really make a huge difference and we never thought about them before. Just imagine going back in time and trying to explain all of these to a bunch of cavemen. We think we know it all, but in reality, we are pretty clueless about details around us.