E911 is a technology that uses cell towers to locate. If you’re trying to locate your loved one, the product will send out a signal to the cell towers. The three nearest cell towers triangulate to a calculated position. It is not very accurate. It is an approximate location. Cell phone companies use this technology for their GPS tracking. The location often changes within seconds. The best way to get accurate information is to use GPS. Using a combination of GPS and E911 is the best approach to positioning an individual in the market today.