A favorite pastime of Internet users is to share their location: services like Google Latitude can inform friends when you are nearby; another, Foursquare, has turned reporting these updates into a game.

But as a German Green party politician, Malte Spitz, recently learned, we are already continually being tracked whether we volunteer to be or not. Cellphone companies do not typically divulge how much information they collect, so Mr. Spitz went to court to find out exactly what his cellphone company, Deutsche Telekom, knew about his whereabouts.

The results were astounding. In a six-month period — from Aug 31, 2009, to Feb. 28, 2010, Deutsche Telekom had recorded and saved his longitude and latitude coordinates more than 35,000 times. It traced him from a train on the way to Erlangen at the start through to that last night, when he was home in Berlin.

Mr. Spitz has provided a rare glimpse — an unprecedented one, privacy experts say — of what is being collected as we walk around with our phones. Unlike many online services and Web sites that must send “cookies” to a user’s computer to try to link its traffic to a specific person, cellphone companies simply have to sit back and hit “record.”