now the app isnt meant for this.. but hands-down this is the slickest way for tracking... youd just install this on your own device, give out the codes you only want used... then if they cant reach you on a ride, all they have to do is send a text command and theyll get your gps location thats able to be opened in google maps..
i used to use this as my anti theft software.. the app can do some evil stuff if used in vain so it kinda got a bad rep.. check it out yourself, but Phone Creeper will do what you want..
http://forum.xda-developers.com/showthread.php?t=527423