I wonder if an argument could be made that this violates the 4th amendment right to be free from unseasonable search. Collecting your travel movements automatically without cause might apply. It is an interesting problem because there is no expectation of privacy in public. If you venture into public the police or anyone can stake you out and take pictures of you. Devices that do this are just an efficiency increase. The true root of the issue might be whether the government has a right to collect information about you at all. Before taxes about 100 years ago they really had no reason to.