The FBI describes its device as a "wireless router monitoring device” that captures addressing and signaling information and transmits it wirelessly through the air to FBI agents watching the home. It was installed the same day and was soon showing agents what Hammond was up to online.
I'm curious about this device; it would have to be able to fully decrypt 802.11 frames just to be able to see the layer 3 IP information, so in theory it is able to see all of the traffic but the agents aren't allowed to look at (or use) anything beyond the IPs because that would be considered wiretapping. I have to imagine the guy arrested was technically competent enough to use WPA2 with a fairly strong non-dictionary-word key, yet this device was able to crack that key in a short enough amount of time for this sting operation.