I am trying to build a simple datalogger that will record the temperature in my home and if I am home or away. I travel a lot for work, and when I leave I unplug my router - this will be how I determine if I am home or away.
Is there a simple way to have my Arduino determine if the router is on or not by monitoring a couple wires on an unused port? I don't have an ethernet shield, looking to do this with nothing more than an optoisolator if possible.