When I woke up the other day, I went straight to my computer to catch up on the news and read e-mail. About 20 minutes later, I walked half a block to the gym, where I exercised for 45 minutes. I took the C train to The New York Times building, and then at the end of the day, I was back on the C train. I had dinner on my friends Elisabeth and Dan’s rooftop, then walked home seven blocks.

I’m not giving away any secrets here  nothing I did was secret to begin with. Verizon online knows when I logged on, and New York Sports Club knows when I swiped my membership card. The M.T.A. could trace (through the MetroCard I bought with a credit card) when and where I took the subway, and The Times knows when I used my ID to enter the building. AT&T could follow me along the way through my iPhone.

There may also be videotape of my travels, given the ubiquity of surveillance cameras in New York City. There are thousands of cameras on buildings and lampposts around Manhattan, according to the New York Civil Liberties Union, many near my home and office. Several may have been in a position to film dinner on Elisabeth and Dan’s roof.

A little-appreciated downside of the technology revolution is that, mainly without thinking about it, we have given up “locational privacy.” Even in low-tech days, our movements were not entirely private. The desk attendant at my gym might have recalled seeing me, or my colleagues might have remembered when I arrived. Now the information is collected automatically and often stored indefinitely.