What expectation of privacy do you have?

Two years ago in New Bedford, a heated street argument left a bystander dead from a gunshot wound. Police were aided in piecing together what happened by an audio  recording made by ShotSpotter, a system of microphones deployed across the city to detect and pinpoint the sounds of gunfire. Not only did ShotSpotter do that in this particular case, but a recording of the argument was made. 

In Mansfield and other cities and towns across Massachusetts, a police cruiser equipped with an automated license plate reader runs the registrations of every car it drives past. The stored data can also come in handy in investigations. For example, if a house was broken into, police can review who was parked in the area the last time the specially-equipped cruiser drove by. 

In 2001, Tampa used facial recognition technology to scan Super Bowl attendees. Other cities, airports and gathering places have also experimented with this technology. Logan Airport's experiment yielded a lackluster 61.4% accuracy rate. Private companies are also getting in the game. I'm typically reminded of this when I post pictures to Facebook and get accurate tagging suggestions. 

There's no question that technologies like these help law enforcement be more effective. But what is our expectation of privacy - and what should it be? I'm not talking about people who have acted in such a way as to invite police attention to themselves. I'm talking about you and me. 

The Fourth Amendment recognizes our right to be secure in "...our persons, houses, papers and effects against unreasonable searches and seizures..." Over the years, court decisions have painted the picture of where you have an "expectation of privacy." You don't have an expectation of privacy in the substance of what you say when you're yelling at someone on a public street. You don't have an expectation of privacy in what your license plate says. And you don't have an expectation of privacy in what your face looks like when you go out in public. On the other hand, the Supreme Court has held that a GPS device can't be attached to your car without a warrant, and they may render a decision this term on a Massachusetts case involving a warrantless search of the cell phone of a man in police custody.

We might expect to occasionally drive past a cruiser that runs our registration, but do we reasonably expect scrutiny far beyond the manpower capability of a local police department if they were limited to traditional, manual police work? If we don't know that a particular kind of technology exists - much less that it's being used on us right now - can we reasonably expect that it won't be used on us? 

Against the backdrop of the NSA scandal and other examples of governmental interest in our daily lives, it's understandable that many view technology like this with a healthy degree of suspicion.