@n3by:
@NOYB
why don't you use Captive Portal for that ? It add another layer of security for your network.
Nice suggestion but take this further, when you dont have total oversight of the physical network ie cables or insides of a device with wifi capabilities namely a laptop or mobile plugged into synch with a computer especially in a bring your device to work scenario, there is still the situation of a device/code hijacking one or more machine(s) and off loading the network traffic via a wifi/mesh network of sorts.
In this instance only the absence of traffic at best will show up in pfsense if all traffic is rerouted via a dhcp/dns redirect, although if only off loading sensitive data you wouldnt even spot this potentially*, abit like a multi wan set up but on the device in question or would you?
I can think of one situation which could theoretically show this up, but its not something pfsense could do and the OS'es could still potentially be the weakness.