I was wondering if it were possible to have two cellphones interact with one another like a radar/sonar device to be able to find one another or be accurate within maybe 500 yards or so? Also, if there is a way to do it without the GPS or connecting to a cell tower (like being indoors or out in a desert)? Are there any technologies resident in a cellphone that can bounce off each other link radar to find one another basically without the need for gps/cell tower triangulation? Im trying to create a fun app similar to the Ghostbuster's EKG Meter :-)
Wifi direct can reach further than Bluetooth and also transmit data faster http://developer.android.com/guide/topics/wireless/wifip2p.html
But 500 yards seems to be too far for the technology reside in the current mobile phone.