Google does let you limit sharing to only your city-level location, and in both apps you can enter a (possibly false) location for yourself.

Both Google and Loopt say they do not store historical locations, only your last location. That's important in case someone-the government, say, or a civil litigant-seeks that data. Loopt says it will share that info only under a wiretap or­­der. Google hasn't said it will do the same, but it does have a record of fighting government requests for its users' information.

My conclusions? Some things could be improved: First, you should be able to share your location only for a set amount of time-say, the next 2 hours, or from 6 to 9 p.m. on Fridays. Loopt says that ability will come in a future release, but Google isn't planning to announce anything along those lines.

Next, I think Google should have an auto-shutoff after a certain amount of time, in case you become forgetful. And it should explicitly declare it won't share your information without a wiretap order.

Of the two, you might try Loopt (ideally on an iPhone), since it has auto-off and will also come out with time-based controls.