It depends...
Recently, I got myself a modem/router/WiFi box, because I had got bored with only being able to connect two machines at a time. I.e. I was using an old USB modem for my broadband, and a crossover cable when I wanted a second machine online.
I had also just got my Acer Aspire One, and wanted that to connect via the WiFi (which I didn't have).
Now, when I got the router, I had some hassle with getting my Apache webserving working properly, so I fell back on using the USB modem for the broadband, instead of the router box.
With that setup, it would be easy to monitor access, as I could just log the stuff accessed via the USB modem on that machine.
However, with the router connecting the WiFi directly to the broadband, you would need to patch into the router box to see what was going on. Not so easy. My Zoom modem allows a fair amount of tinkering, but I don't think I can monitor the direct WiFi to modem connections at the level you are talking about.
_________________
"Striking up conversations with strangers is an autistic person's version of extreme sports."
Kamran Nazeer