Simon, the short answer is yes you do.
Download a piece of free software called NETSTUMBLER. Fire this up and it will detect ALL networks within range including your own. It will tell you whether they are secured, it will give the name of the network and the channel they are on. It will also give signal to noise ratio.
I live in a fairly detached house, ie not in a modern close community. My nearest neighbours do not have wifi. The nearest possible after that are 60 m or more distant. My own signal does not reach across my house through 4 walls which just goes to show how you might think you are safe.
Some networks that I have stumbled on have generic or default names like Belkin or Linksys. With names such as these a 'war walker' already has an IN as the Admin feature will probably be left with the default password.
Others actually use the house name or the name of the user. Chuck's for instance would enable more direct targeting and you may even be keener to hack into Chuck's than Joe's.
More legitimately Netstumbler enables you to deconflict from other channels and also try different channels to get the best signal to noise ratio.