Using a cell phone to dial 911? Here is what happens.

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According to the California 911 Emergency Communications Office, well over half of all 911 calls come from cellular phones. In the past, cellular 911 calls were automatically routed to California Highway Patrol 911 dispatch centers, overloading these call centers and causing many callers to receive a busy signal instead of a 911 dispatcher. Today, when San Ramon residents dial 911 from their cell phone, a majority of these calls are routed directly to the San Ramon Valley 911 Communications Center.

The routing of these cellular 911 calls is made possible through technology known as Enhanced 911 which uses data collected almost immediate when a cell phone is used to dial 911. The location of the primary cell tower being used, cell tower triangulation, and GPS information from the cell phone itself is instantly analyzed so the local Public Safety Answering Point (dispatch center) can be identified and the call is routed to the proper location.

As with all technology, there are a few things to keep in mind which will influence these calls. If a cellular 911 caller is on, or in close proximity, to a freeway, there is a high likelihood this call will go to the California Highway Patrol dispatch center. The California Highway Patrol (CHP) has jurisdiction over state freeways and handles emergency calls on these roadways. Cellular calls often utilize towers that are located near the freeway. Therefore, some cellular calls made from city streets, but near a freeway, will be routed to the California Highway Patrol. As an example, if a resident calls 911 from the In-N-Out parking lot on San Ramon Valley Blvd, there is a chance that call will be first routed to the California Highway Patrol dispatch center.

Also, if there is an significant incident on or near the freeway, multiple cellular 911 calls may overwhelm the closest cell tower. When this happens, cellular calls are routed through other nearby towers. Occasionally, this means the cellular phone’s location may not be as accurate because the cell tower triangulation information can be misleading. This inaccurate information may cause the call to be routed to the California Highway Patrol dispatch center before it is transferred back to the San Ramon Valley 911 Communications Center.

San Ramon residents, or those visiting or working in San Ramon, can always use our non-emergency line (925-973-2779) to directly reach police and fire. If you call this number, you will always get the San Ramon Valley 911 Communication Center, regardless of whether the call is make from a landline or cellular phone. Please remember though, if you are traveling outside of the San Ramon area and experience an emergency situation, always dial 911. Your cellular 911 call will be routed to the local agency, providing quicker and more efficient emergency service.

If you would like to know more about the San Ramon Valley 911 Communication Center, click here. The dispatch center is a joint partnership between both the San Ramon Police Department and the San Ramon Valley Fire Protection District and was designed to improve emergency response times to better serve the San Ramon community.


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