title: Way(s) to detect nearby mobile devices using the Android SDK?
body: <p>I'm contemplating the development of an Android app that detects all or most nearby mobile devices (iPhone, Android, etc) in the immediate neighborhood that are turned on. I don't need to interact with these devices, just detect them, and a requirement is that the detected devices can't need to have any special / unusual apps installed on them. The app only needs to work for typical U.S. devices and networks.</p>
  
  <p>I've thought about a few ways to do this (somehow detecting bluetooth, wifi, or cellular transmissions / identifiers), but I'm looking for specific implementation methods for a way to detect a relatively large proportion of nearby devices. I'm not sure which of these methods is possible / feasible or how to put them into practice...</p>
  
  <p>Perhaps using Bluetooth: Is there a way using the Android SDK to detect non-discoverable Bluetooth devices (not in discoverable mode)? <a href="http://www.developer.nokia.com/Community/Wiki/How_to_detect_a_bluetooth_device_being_in_non-discoverable_%28private%29_mode" rel="nofollow">The Nokia Developer site seems to suggest this is possible using Service Discovery Protocol (SDP)</a>, but I'm not sure if this is possible more generally in Android. </p>
  
  <p>Perhaps using cell tower mast switching simulation? Ok, this is almost certainly beyond the reach of Android, but <a href="http://www.ideasproject.com/ideas/3546" rel="nofollow">this article suggests that there may be a way to "mimic cell mast switching process to trigger quiescent phones into transmitting. Phones respond with their ID and authentication signals..."</a>.</p>