Okay, so basically i need a way to alert me if someone unwanted is around me. I mean I'd have a list of whitelisted people (devices). If anyone except these are found around i want the app to alert me. I know the privacy issues. I don't want any of their device's info or something. I just need to know about someone's presence. How can i detect that? Now to detect the phone I need some signal coming out of it (leaving bluetooth,wifi,hotspot) is there any other source of signal that i can interpret? Can i detect a network signal?( I mean to just detect a mobile network signal around me (Not communicating or tampering). OR Can i detect increase in network congestion around me(implying someone around me).Is this a security concern? Hope you understand what i intent. If there is any other way please help me.