Family Tracker is a new iPhone app that allows you to track your wife, husband, or children using your mobile device's GPS feature-- the app requires the consent of the person being monitored for those of us concerned about privacy. 

Compatible with iOS 4, the mobile app runs in the background, constantly updating the uesr's location. Spouses can therefore instantly know their partner has safely reached their destination at home, work or during long trips, asserts the developer behind Family Tracker, LogSat Software. And parents, for example, can know if their children are exactly where they should be, and didn't sneak out without permission.

The location can be viewed on an iPhone or through any desktop web browser.

Family Tracker (download) goes for $3.99. By contrast AT&T offers a similar service that costs $14.99/month.