Authorities aren't restricted from using a lie detector in the US, just from using the results in court. They're frequently used to pressure suspects in criminal cases during questioning, knowing the results are inadmissable.
It's most probably meant for opportunistic sensing in industrial environments, where it might become quite useful. It's not something you're going to use at home.
Since this is passive sensing, an attacker outside your home can make use of the WiFi signals emitted from the router inside your home. Or they can broadcast their own signal.
