Google has expanded its Latitude service, which allows users of Google Maps to pinpoint the location of friends and family, so it can also be used to contact them via SMS, Google Talk or Gmail.

The sevrice, which was launched in February this year, is also able to keep track of your location history so you can look back on where you've been, according to a blog by Chris Lambert, a Google mobile software engineer.

The company also is unveiling the beta of a new feature called Google Location Alerts, which is designed to let you know when one of your friends is nearby.

For the location history, users should be able to play back their recent locations in order or view them on Google Maps or Google Earth.

If you don't want anyone else seeing where you've been, Lambert notes you can delete specific locations or your entire location history.

"Whether you're taking a road trip across the country, backpacking across Europe, or just going out for a night on the town, it's fascinating to look back at where you went, and for how long you stayed," said Lambert.

"Enable Google Location History to store, view, and manage your past Latitude locations... I stopped at an awesome BBQ place on my way back from Lake Tahoe this summer, but I couldn't remember the name when my friend was asking about it a few months later. I pulled up my location history for that weekend, found where I was stationary on the drive home, and the restaurant name showed up in Google Maps: Drooling Dog Bar BQ. "

With Google Location Alerts, Lambert said Google didn't want to make the service annoying by sending too many alerts, such as receiving a notification every time a co-worker walks into the office building, or a spouse or a roommate returns home.

"To avoid this, we decided to make Location Alerts smarter by requiring that you also enable Location History," Lambert said.

"Using your past location history, Location Alerts can recognise your regular, routine locations and not create alerts when you're at places like home or work. Alerts will only be sent to you and any nearby friends when you're either at an unusual place or at a routine place at an unusual time. Keep in mind that it may take up to a week to learn your 'unusual' locations and start sending alerts."

Privacy advocates haven't had much time to review the new features, but they were concerned about the original version of Google Latitude.

Last February, Privacy International called Latitude a "danger" to security. Critics said at the time that the new feature lacked sufficient safeguards.

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See also: Google Latitude for iPhone launches as web app