It's geared toward worried parents and suspicious bosses and might seem Orwellian to some: the first major commercial service that traces people's locations using their mobile phones.
The mapAmobile service, launched last month across Britain, charges $48 a year, plus about 50 cents per request. It claims accuracy to within 50 yards.
Even more precise services are likely in the United States within the next year as more phone models come with global positioning system chips already installed.
The Carphone Warehouse PLC, which runs the British service, touts it as offering parents peace of mind or allowing businesses to check on the whereabouts of staff.
"We are responding to a real consumer need by bringing to the market a reliable, affordable and effective way for people to locate each other without disturbing them," said chief executive Andrew Harrison.
The consent of the cell phone owner is required, said Harrison. Even so, privacy advocates say there's potential for abuse.
"Given that we know that schoolboys have hacked into the Pentagon computer, nothing is secure," said Barry Hugill of the rights group Liberty. "Once the technology is there, it is there to be abused and I find it very hard to believe that it would be watertight. Potentially we could see stalkers moving in on the act."
The service is available from Britain's four main wireless operators, Vodafone Group PLC, Orange SA, mmO2 PLC and T-Mobile International AG, and smaller operators Virgin, Fresh and 3 Mobile are expected to join too.
Kate Marriot of the Mobile Data Association, an industry association, said mapAmobile was the first service "to be launched on such a large-scale commercial basis."
MapAmobile locates users by tracing the unique identifier each cell phone transmits and triangulating between the network towers that transmit and receive signals to and from phones.
Law enforcement agencies have used this method to track suspects for years, though accuracy varies between urban and rural areas. Last year, the FBI arrested a man accused of planting pipe bombs in Midwestern mailboxes after he turned on his cell phone in Nevada.
Location requests can be made to mapAmobile using text messaging, by calling a toll-free number or on the Internet. It is available 24 hours a day, but will only work if the mobile phone of the person being traced is switched on.
The provider says safeguards are in place to protect civil liberties. Not only do cell phone users have to consent to being tracked, they are sent regular text messages reminding them their phones can be traced and that they can request a list of people who can locate them.
Niki Torrance, a spokeswoman for MI International, the British company that created the technology, said thousands of people have signed on.
Torrance also said her company is talking to potential partners in the United States and continental Europe, and said the service could be available to U.S. consumers this fall.
Similar tracking services that aim to help parents or caretakers are already available in the United States using GPS technology, including Digital Angel, which uses a pager-like unit worn by the person being traced.
GPS is more accurate than cell phone tower triangulation, which is why it is being added to many new phones to help emergency crews respond to 911 calls from wireless phones.
As more phones get such chips, some U.S. wireless carriers are exploring using them to offer location-tracking services similar to mapAmobile.
Verizon Wireless, the largest U.S. carrier, could launch such a service next year, spokesman Jim Gerace said. He said it could be popular among companies with big vehicle fleets that want to track the positions of their drivers.
As for privacy, Gerace noted that it is very easy for users to set their phones so they transmit GPS information only on 911 calls.