I just downloaded an app for my phone called CRADAR, the way it works is you turn your GPS on when you start hunting and select a emergency contact. If (God forbid) you should fall from your treestand it will activate the program and start a countdown which can be set at different lengths, once the countdown expires it sends your emergency contact a text message that says you have fallen and may be injured plus your GPS coordinates. Its available for android based phones, dont know about Iphones.