Most of pr2_computer_monitor exposes no public API.
network_detector is a small node which watches a network interface (such as eth0) and publishes whether it is connected or not.
network_detector requires a single parameter, "network_detector/interface_name", giving the name of the interface, for example "eth0" or "wan0".
The output is a single boolean on a topic called "network_connected". It is a latched message which is published about every 5 seconds and whenever the status changes.