As has been, CNET Reviews editor James Kim and his family disappeared in Oregon during a Thanksgiving road trip. James' wife, Kati, and their two children, Penelope and Sabine, were found safe Monday afternoon. The body of James Kim, who left his family on Saturday in search of help, was found Wednesday.
Authorities conducting the search said at a news conference Monday that a signal sent from the Kims' mobile phone to a tower in the region was key to locating the family.
The search for the Kim family is the latest example of how important cell phone technology has become as a public safety tool.
While other technologies such as global positioning system, ormay help people find their way out of trouble, it does little to help when people are stranded on the side of the road like the Kims were. Tracking devices that send beacons to rescuers could be helpful, but they are used mostly by wilderness backpackers and backcountry skiers. Few people carry them on road trips. And even though satellite-based tracking technology exists, even fewer people are likely to consent to having their whereabouts tracked on a daily basis in the off chance that they might get lost on a backcountry road.
At the end of the day, the technology that has proved the most valuable for locating lost or missing people has been cellular phones.
"Navigation tools may help someone if they need to understand where they are to get to safety," said Kiyoshi Hamai, director of sales and product management with Mio Technology, a company that sells portable navigation devices using GPS technology. "But in order for someone to find you, you really need a device, like a cell phone, that can provide two-way communication."
Even General Motors' OnStar service, which provides GPS navigation and tracks cars when they are stolen, relies on a cellular network to communicate with the GPS receiver in the car.
"We don't communicate with our in-vehicle OnStar device via satellite," said Steve Davis, Service Line Manager for the OnStar Personal Communications service. "We connect to the device through a cellular phone connection. And if we can't connect to it through the cellular network, then we can't retrieve the GPS location information stored in the device."
So how does it all work? Mobile devices, when they are within range, constantly let cell towers and the mobile switching center, which is connected to multiple towers, know of their location. The mobile switching center uses the location information to ensure that incoming calls and messages are routed to the tower nearest to the user.
If a subscriber is unable to get service, this location information is usually purged from the mobile switching center. But some location information may remain in call detail records. Some mobile operators may store the most recent communication between a device and a mobile switching center for a certain period of time, usually 24 hours.
When someone is missing, even this small bit of information can prove useful in determining the approximate location of a device using the updates from the mobile switching center. If the mobile subscriber is still within cell phone range, authorities can track his or her general movement by following the sequence of towers the phone has contacted or pinged. And if the cell phone goes out of range or runs out of battery power, the mobile operator may be able to use the last recorded location before the cell phone either lost its signal or lost power.
But the most useful information for locating people when they are lost comes when someone has initiated or received a call or text message on their phone. Mobile operators keep records of these events for billing purposes in what is known as a call data record, or CDR. And they can go back to these records to get a historical account of the cell phone's location.
This is actually what authorities used to locate the Kims' phone, according to Eric Anderson, director of engineering for Edge Wireless, a regional mobile operator that provides cellular phone service in the area where the Kims were stranded. One of Edge Wireless' cell phone towers briefly connected with one of the family's phones at about 1:30 a.m. November 26 near Glendale, Ore. The phone was connected long enough to the network to send a notice that there was a voice mail or text message waiting. But the connection didn't last long enough for the Kims to retrieve the message or initiate a call for help.
Still, the connection was long enough that two Edge Wireless engineers, Eric Fuqua and Noah Pugsley, were able to find this information in the CDR to determine that the family was in sector "Z" in the southwestern portion of the cell site's 26-mile radius. Wolf Peak's "Z" sector provides coverage to remote areas with little population and very little cell phone traffic. Using this information, authorities sent out rescue teams, which eventually located Kati Kim and her children.
Anderson said that the family was lucky that they were Cingular Wireless subscribers. Edge Wireless uses the same GSM network technology that provides roaming coverage to Cingular customers. If the Kims' phone had been with a different provider that didn't have roaming coverage with Edge Wireless, then the company might not have received any signal at all after they left the major highway, and the cell phone would have been of little use to authorities trying to rescue them.
"Where the Kims' car was found was on the fringe of our coverage area as it was," Anderson said. "So it was a miracle that the phone was able to lock onto the network at all."
Anderson said that if people ever find themselves in a similar situation--lost and having difficulty getting cell phone reception--they should search for the highest ground or area that may be in the line of sight to a tower. They should hold the phone away from their bodies or high so it has no obstructions to a possible tower. It may take up to two or three minutes for it to synchronize or connect with the cell tower and mobile switching center. Even if they can connect for a second or two, it could be long enough to register a voice mail or text message, which could ultimately help wireless engineers track their location.
The E911 FCC regulations are likely to help rescuers find those who are lost even more quickly, even if people are unable to reach a 911 operator for help.
Phones sold today by Edge Wireless and other carriers using GSM network technology, such as Cingular and T-Mobile, comply with the FCC regulations using network-based technology that calculates a mobile phone's location in real time using signal analysis and triangulation between towers. Wireless carriers using CDMA network technology, such as Alltel, Verizon Wireless and Sprint Nextel, have GPS technology embedded in them to fulfill the E911 government mandate.
Both network and GPS location information allow authorities to send signals or pings directly to these handsets to find an approximate location of the phone.
Some cell phone operators, such as Disney Mobile, Boost Wireless and Helio, are using GPS-enabled phones to. Disney Mobile , while Boost and Helio are marketing their services to appeal to young people who are looking to keep in touch with their friends.
Services that allow people to be tracked either through the cellular phone network or by satellite. But Joe Farren, director of public affairs for CTIA-The Wireless Association, a trade organization representing mobile operators, said that is why people must opt-in to services that allow tracking.
Still, cell phones have their limitations. For example, battery life varies greatly. Some batteries last for several days, while others may lose power after only a few hours.
And even though cellular network coverage has improved tremendously over the past several years, it is still not ubiquitous in the United States. Even some urban areas have dead zones, particularly in buildings or underground. Rural and remote areas suffer most from lack of coverage. And these areas also happen to be places where people are most often stranded or lost.
All that said, Farren believes that cell phones will continue to play an important role in providing safety and security for people.
"Wireless phones are an incredible safety tool," he said. "They are the most valuable tool invented for some time. They save scores of lives. And they will continue to get better."