I have a wireless network that is secured using WPA and my ssid is not broadcast.I don't have any worries regarding the security of my network ,However looking into my routers log there are entries which imply dos attacks, to be honest i don't really understand them.
To put your mind at rest there is a program witch will detect such intrusions with an audible alert shouold someone try to connect to your network click here free.(works with wired and wireless setups)
I have been using it for some time now and not encountered any unauthorised access.
The air horn ( a message sent to the intruder only works if the intruder has windows messenger enabled)