How did your phone know you were even near that particular Starbucks? What else does it know about you?
Enter location tracking, coming to a mobile device near you. Features that one day can pinpoint your whereabouts to within the length of a football field raise enormous privacy concerns, but they also offer enormous benefits.
The challenge will be determining where to draw the line.
Consider a technology to be unveiled Monday. Called Digital Angel, a microchip worn close to the body promises to record a person's biological parameters and send distress signals during medical emergencies.
Cell phones, handheld devices, even car navigation systems will soon have detailed tracking abilities, if they do not already. Services could begin appearing within a year or so.
Much of the drive will come from a federal law that requires cell phones to identify callers' locations to speed 911 emergency responses. If the industry has to install expensive equipment anyway, why not use it also to make money?
"There's going to be a dramatic increase in the amount of tracking that's made possible, in part by services they don't know they have," said Daniel J. Weitzner of the World Wide Web Consortium, which sets technical standards for the Web.
Such tracking will let someone visit a Web site and automatically get weather, movie showings or neighborhood restaurants, based on their current location. If they're lost, they will be able to ask for turn-by-turn directions. Those short of cash can be pointed to the nearest bank machine.
But if the information is stored, location tracking could result in a 24-hour-a-day record of a person's whereabouts.
So what if a divorce lawyer wants to check if someone's been cheating, or if a social service agent wants to know how many times a person has visited a candy store with his child?
"You have to ask, `Who gets how much information?"' said Jason Catlett, chief executive of Junkbusters Corp., a non-profit privacy monitoring group in Green Brook, N.J.
"Telephone records are routinely subpoenaed. They can be very intrusive, but far more intrusive is a complete log of your physical movement."
But companies looking to gain business from location tracking insist that the worst-case scenarios presented are impractical to implement in reality.
"There's no way a database is large enough or cost effective for Starbucks to monitor everyone's location on the offchance they can acquire a customer," said Jason Devitt, chief executive of Vindigo, which offers 11 city guides through Palm organizers.
Lee Hancock, founder and chief executive of go2 Systems Inc., said any short-term gains from such tactics would be offset by losses if they alienate customers.
Leading wireless and advertising companies agre that they must tread carefully because mobile devices are inherently more personal than desktop computers.
At DoubleClick Inc., whose ad-targeting system generated much of the Net's privacy complaints, officials won't deliver location-based ads right away. The company wants to develop privacy standards first, using lessons from the desktop.
"We've all learned what to do and what not to do, and we can port that over to the wireless market," said Jamie Byrne, strategic director for emerging platforms at DoubleClick.
Any such ads will likely target a metropolitan region, rather than a city block, because audiences for block-by-block ads would be too small, Byrne said. Ultimately, he said, such targeting will help subsidize wireless services that customers want.
Jonathan Fox, director of business development at advertising company Engage Inc., says location-based profiles would not carry names and other personal information.
TRUSTe, which runs a seal-of-approval program for Internet privacy policies, is looking to develop guidelines for mobile applications. Details that remain to be worked out include how to notify customers on a phone's small screen.
"It's more difficult to retrofit policies if you're already down the road," said Robert Lewin, TRUSTe chief executive. "Here, we have the opportunity to do it right the first time."
In many ways, a person's whereabouts are already being tracked.
Employee security cards record when people enter buildings. Discount grocery programs track what people buy, where and when. Electronic toll-payment systems know when someone traverses a tunnel or bridge.
Current phones can pinpoint callers to a few miles by determining the location of the cell tower used to handle the call.
Palm VII organizers use similar techniques to narrow a user to a particular zip code, and an optional global-positioning receiver can pinpoint that person even further.
Marketers can also get clues from the items people search for or the sites they visit a city guide, for instance, tells in what city a person is likely located or where they plan to visit.
But for the most part, marketers have yet to take full advantage of such knowledge, and consumers have yet to complain.
"We're providing value," Palm spokesman Ted Ladd said. "Mobile users are inherently in a hurry."
Wireless providers are not likely to have a use for storing location information, except perhaps for applications that help with driving directions.
Paul Reddick, vice president of product management and development with Sprint PCS, said such storage is not practical, necessary or even desirable.
"It takes years to build a brand and build trust," he said, "and you can blow it pretty fast."