Your phone number’s area code gives other people a clue to where you live, or have lived in the past. Startup company Loc-Aid can use your full phone number to figure out exactly where you are right now.

The service has caught the eye of banks and card issuers interested in checking where their customers are—as a way to reduce fraud—and of retailers interested in sending deals to people nearby.

“We can locate any one of the more than 350 million devices on the major U.S. and Canadian carriers in real time,” says Rip Gerber, founder and CEO of Loc-Aid, based in San Francisco.

You can test Loc-Aid’s ability to find your phone using this Web demo. It takes from five to 20 seconds to get a location fix for the device associated with a phone number. “The companies using our service already know their customer’s phone number and just need to get permission from them to use that to find their location—that’s usually done by SMS,” says Gerber.

A person might be prompted to allow such tracking when they use their bank’s mobile website or app, says Gerber. He says that Loc-Aid will ensure that a request for permission is never buried in the terms and conditions of a service and that a user is always told exactly how his or her data will be used.

Loc-Aid’s service is possible because it developed technology and made agreements that aggregate the phone-tracking abilities of every major U.S. and Canadian cellular network, which are legally required to have technology that spits out the location of a device making a 911 call.

Devices are located using the signal strength of nearby cell towers. The accuracy varies from hundreds of meters in areas with few cell phone towers, such as rural areas, but can be to within a block or even an individual building in urban areas.

Earlier this year, Loc-Aid added the final major wireless carrier—T-Mobile—needed to provide universal coverage for the major services in U.S. and Canada, covering roughly 95 percent of North American cellular devices.

“Now we have enough of a footprint that the service becomes very interesting and useful,” says Gerber. Loc-Aid is running pilot projects with one major credit-card issuer and several banks; these companies are interested in locating users in order to cut fraud. It costs such companies hundreds of millions of dollars to run a call center to contact people when their cards trip fraud-detection alarms. Checking the location of a person’s device may offer a quicker and cheaper way to identify potentially suspect transactions.

AT&T is using Loc-Aid to offer school districts a way to track students with a history of truancy. Other trials are using the technology as an alternative to tracking parolees with GPS anklets, which can easily lose signal when indoors.

Current trials focus on applications where there is real money at stake, because each location lookup costs money, and Loc-Aid passes on that cost. However, Gerber says the cost of location fixes is set to drop, and that carriers are working to dramatically improve how accurately they can locate phones. This could open up new ways for the service to be used, for example in mobile apps and other services used by consumers as a less battery intensive alternative to GPS.

“Next year, carriers will begin to offer new levels of mapping where they will be able to know where a device is to within a five-meter accuracy in some places,” says Gerber.

Exact details of how this will be achieved have not been made public, but Gerber says that cell companies could be thought of as “doing war driving on their own network.” War driving refers to the practice driving around while noting the characteristics of wireless networks in different places. The results can be compiled into a database of signal strengths for different locations that can be used to work out a device’s location from what it can detect around it. Apple controversially had iPhones “war drive” Wi-Fi data to boost its own location database.

André Malm, an analyst with Berg Insight, in Gothenberg, Sweden, agrees that the cost of locating mobile phone users in this way is likely to drop. “They are using these legacy systems today but will add new ones that support very high numbers of lookups,” he says.

As the cost drops, consumer-facing apps and websites could also start using the technology, says Malm. “When being located doesn’t have to be instigated by the user opening up something on a GPS device, [then] apps and Web-based services can try new things.”

Vincent Blondel, a mathematics professor at Université catholique de Louvain in Belgium, who researches extracting useful data from call and location records from cellular networks, says that Loc-Aid is opening up access to data that usually remains inside wireless carriers. “Location data has enormous value,” he says, although companies are still trying to work out how to put an exact figure on it. “The value may depend on the time of the day, and perhaps also on location,” he says.

Loc-Aid’s Gerber acknowledges that such data must be handled carefully. “Subscriber permission to use mobile location will only continue if users trust the apps, the carriers, and all players in the mobile ecosystem,” he says. However, Blondel says recent research suggests it can be very hard to truly anonymize location information.

Seeing the amount of location data that wireless networks record about customers can be surprising, say Blondel, citing the striking maps obtained by German politician Malte Spitz, who requested access to the location data recorded by his cell-phone network provider.