You press a button and, several rooms away, something makes a sound. That sentence hides one of the loveliest chains of physics in your house. Your fingertip closes a gap between two metal contacts, and the moment they touch, electrons that were pooled and waiting begin to drift, not fast, mind you, the individual electrons crawl through copper slower than you walk, but the field that pushes them propagates down the wire at nearly the speed of light.
So the news of your finger reaches the chime almost before your finger has finished arriving.
And what makes the sound? In the old ones, an electromagnet yanks a small iron rod, which strikes a tuned metal bar, and the bar rings because you have just handed it energy it doesn't want. It sheds that energy the only way it can: by shoving on the air, packing molecules a little tighter, then a little looser, a pressure wave rippling out at 343 meters per second until it wobbles the eardrum of whoever is home.
"Someone is here" is not a message. It is a bar of metal shivering.
Consider the copper carrying all this. Every atom in that wire was forged inside a dying star, fused under pressures your kitchen cannot imagine, then flung across the galaxy when the star came apart. It drifted for billions of years, condensed into a rock, got dug up, drawn into filament, and stapled beside your door.
The whole apparatus sits idle for weeks, storing a tiny voltage, patient.
Then a stranger arrives, and starlight that spent an age becoming a doorbell spends a quarter of a second telling you they'd like to come in.