Wi-Fi devices that people use for home networking have radios built in. And it's via radio waves that the miracle of wireless networking takes place.

A home Wi-Fi device generates radio waves that are sent out in 360 degrees, like the ripples that radiate across the surface of a pond when you throw a rock into it. These radio waves go right through the walls of the house, and out into the world at high speed.

At some point in their journey, Wi-Fi radio waves breach the private-public barrier. They wash over your privately owned lawn before continuing on over the publicly owned sidewalk and street.

A person walking or driving by is physically penetrated by these waves. (Some studies have suggested that the waves may increase the risk of cancer; they probably don't.) The radio waves enter people's bodies, are conveyed through their bodies, and then continue on their journey on the other side.

Wi-Fi radio waves also trespass onto other peoples' private property. If your laptop can see the name of your neighbor's Wi-Fi, that means he is broadcasting radio waves over your property line, through the walls of your house and into your home.