Cell Phone Location

Does 911 know where I am if I call from my cell phone?

Many people trust their cell phones to help locate them when they are lost or are unsure of their exact address when they call 911. Should these people trust their cell phones? Can your cell phone help 911 locate you? The only accurate answer is: Maybe.

Here in Gallatin County, our 911 Center has been Phase 2 Wireless for several years. This means that the wireless companies and the 911 Center worked together to install technology that makes it possible for dispatchers to see the latitude and longitude of where the wireless caller is located. In a perfect world 911 would receive the correct location of the caller every time. But this isn’t the case.

The wireless carriers send quite a bit of information whenever a caller dials 911 from their cell phone. We can receive the call back number of the cell phone, the name of the wireless carrier that owns the cell tower and their phone number, the latitude and longitude of the cell tower, the sector of the cell tower that is being used, the time of the call, and the location of the wireless phone itself—accurate to within a certain number of meters. The tricky part about receiving all of this information is that it doesn’t necessarily come in all at once.

When referring to the location information from cell phones, we usually talk about it in phases. These phases can match how the technology was implemented. For example, in Phase 0, the wireless carriers direct 911 calls from callers to a 911 Center that is appropriate to where the tower is located. If the tower is in Gallatin County (and not near West Yellowstone) it should send the call to Gallatin County 911. In Phase 0, no information accompanies the 911 call. In Phase 1, the 911 Center receives information along with the call. Phase 1 information includes all of the information listed above exceptthe location of the caller. It is very common for the call to come in to the 911 Center with only Phase 1 information. Wireless carriers do this because Phase 2 information can take time to generate and send to 911. Anyone calling 911 should not have their call delayed waiting for the information to catch up with the call.

Phase 2 information, the latitude and longitude of the caller, may be available to 911 after the call has been connected (it may take several seconds or more than a minute). It is also possible that Phase 2 location information is never available, in some cases being blocked by buildings or other large structures. If Phase 2 location information is available after the call is connected, the dispatcher accesses it by requesting a “re-bid” from their phone system. It can take several seconds for the information to come in if it is available. For this reason, it is very important that wireless callers stay on the line with 911 to give us ample time to access the Phase 2 location information. But how accurate is this location information if it does come in?

In Gallatin County, we have had Phase 2 caller location information that was within a few yards of the caller or within several miles. Knowing the exact location of the caller who is in need of help is the only way we can send help quickly. For this reason, we will always attempt to confirm a location with the caller if at all possible. If the caller is unable to confirm a location, we will send help to the closest possible location according to the information we have available. Depending on the accuracy of the location information, help can arrive within minutes or, particularly if the caller is on a trail in the backcountry, can take hours or more than a day. Through our experience with wireless Phase 2 data, we have also found that the kind of technology that wireless carriers use to determine the location of callers can make a tremendous difference.

Wireless carriers can use GPS or triangulation to determine the location of the callers that use their towers. Verizon, for example, uses the GPS location from the phone itself to determine the location. AT&T towers in Gallatin County use triangulation which employs the network of towers to calculate the location. The federal laws accept either method, so wireless carriers choose which way to generate the data. The Federal Communications Commission (FCC) requires that with a GPS based solution, such as Verizon, the location should be accurate to within 50 meters 67% of the time, and should be accurate to within 150 meters 95% of the time. As for network based solutions, such as AT&T, the FCC requires the location is accurate to within 100 meters 67% of the time, and within 300 meters 95% of the time. As proven by the FCC requirements, GPS based solutions are inherently more accurate. Here at Gallatin County 911, we have found this fact to be supported by actual phone calls from both wireless carriers. If all of this is true, then what should you do as a 911 wireless caller who needs help as soon as possible?

The first thing you should do is stay on the line with the 911 dispatcher to allow enough time for your location information to come into dispatch. The second thing you can do is know your location so you can confirm what the technology is telling us. As an alternative, you may want to install a GPS application on your smartphone and know how to retrieve the latitude and longitude of your location. Most importantly, don’t depend on the technology to save you in an emergency. If everything is in your favor, it can do just that. But maybe it’s that one day when it can’t help you.