"That's unreasonable" isn't an argument. What's reasonable is decided by society. New technologies may change what's possible, and make something that was ok before the means to achieve something entirely new.
If, for example, these gadgets, or existing security cameras started to pool their data, run (accurate) face-detection on it, and start publicising everyones' location history online, I'm pretty sure most people would object to that–even those that previously had no problem with their image being recorded by the CCTV at the gas station, or the tourist taking a photo that included them.
"Remember, even if you’re in public, you cannot record conversations between two people unless you have their permission. This includes conversations that you’re one of the parties to. If one person in the conversation can reasonably expect his or her conversation to be confidential, this standard applies."
If you're having a private conversation in a public park, then it is probably illegal for somebody else to record you.
Driving is a different question. Personally I think since a license plate is literally meant to publicly identify your car, a reasonable person should expect it to be recorded. But my guess is this will go to SCOTUS at some point, since privacy is increasingly being invaded in unanticipated ways by private companies.
That's not really a response to matt4077's argument, which is that what a "reasonable person" may think can change based on changed circumstances such as development of new technological possibilities.
Depends on where you live. In Germany any CCTV recording of a public place is automatically illegal. There’s a handful of exceptions (for example, for the parliament), but generally, this holds true.
Opt-in is what’s legally required, and should be the default.
Unless there is a specific situation that there is a threat there, and a warrant for that situation, no.
For traffic situations there are specialized systems that open a physical filter in front of a camera lens only if someone is detected to be speeding, and the camera is then limited to that lane, for that short moment.