Google has updated its Latitude service, which tracks you and your friends' locations, to include a history of the places you have visited and alerts to let your mates know you are nearby.
The Google Location History will store, view, and manage your past Latitude locations. Once this information has been accrued, you will be able to see a visual plot on Google Maps of the places you have been.
Alongside this is something called Location Alerts. Although this feature has been around for some time, it's been updated to be smarter.
Instead of notifying friends every time you step out of the door, it will only notify your Latitude buddies if you happen to be in a place you are not normally in or at a regular jaunt at a different time.
Latitude is still only available on phones, and for privacy's sake you have to enable each new feature you want to use. But if you fancy jumping through these hoops and bringing about a bit of live-streaming to your life, then log on to google.com/latitude/apps for more information.