You can install a standard AP that allows ping and a Wireless Ethernet adapter that are running over the WiFi and this unit as a IP that you can ping...
So...
If the AP answer's to ping everything ok from Internet to the AP and if the Ethernet adpater answers even the WiFi part is ok...
And you should use a monitor software to monitor it every 5 minute or so...
there a lot of these around...
A big systemfor that is NetCrunch from Adremsoft (
www.adremsoft.com) they also have SMS notification... as a alert action...