[lemonlyman87]

I think the reasonableness issue comes into play in two ways:

First, its an objective test, which means reasonableness is based on factors such as democratic accountability, personal autonomy, threats of government abuse, etc.

Second, it's only "reasonable" at an individual level to expet your public locations are being logged if you expect the police have the resources to put a tail on every person in America, which is crazy (Kevin Bankston and Ashkan Soltani have a great paper on "costs" of surveillance and location tracking specifically: http://www.yalelawjournal.org/forum/tiny-constables-and-the-...). The aggregate effect of monitoring everyone's location is a very new concept, and appears very unreasonable based on social norms.

As far as arbitrariness of drawing lines, I think a clear distinction can be made in use of electronic devices to generate location data (in establishing a legal standard the question gets more complex; I recommend looking at writings on topic by Prof. Susan Freiwald, who has done excellent research on the issue). Basing a rule on use of electronic devices is the path states are going down to address both demands for cell phone location data, and directly obtaining location data through devices such as stingrays. It's a simple approach with a clear line that directly gets to the problem of electronic generation of data giving the government unprecedented power regarding location data.

[drivingmenuts]

Stingrays actively attract signal by posing as cell-towers, though, which is different from cameras, which only passively collect images.