What if it's passive? Wifi from the routers of homes emit the RF energy and all the police do is use a detector I could see that as legal since it's energy being emitted just as if it were light shining out a window and you were a silhouette.
>The system, devised by Karl Woodbridge and Kevin Chetty, requires two antennae and a signal processing unit (i.e. computer), and is no larger than a suitcase. Unlike normal radar, which emits radio waves and then measures any reflected signals, this new system operates in complete stealth.
http://www.extremetech.com/extreme/133936-using-wifi-to-see-...
>The system, devised by Karl Woodbridge and Kevin Chetty, requires two antennae and a signal processing unit (i.e. computer), and is no larger than a suitcase. Unlike normal radar, which emits radio waves and then measures any reflected signals, this new system operates in complete stealth.