Just to compensate for my gripe about WiFi Inspector, I want to balance things by saying what a superb performer Avast Free is. Subjectively it does not reduce the speed of a Core Duo 1.67GHz powered 4GB RAM Toshiba Satellite Pro P200 laptop one jot. To add to that, its malware detection ratios are c.100% and I would say that the irritant warnings are a price worth paying. I compared it with Windows Defender and BitDefender Free and both made for a preceptibly slower Windows 8.1 system. I could almost believe that Avast Free actually makes a system quicker than when it has no anti-virus installed. 
I do hope that WiFi Inspector will soon state computer names in addition to MAC addresses whenupon my Avast cup will run over.