Now that some town police departments have started using systems such as Vigilant Video to routinely scan random license plates in search of unregistered or stolen vehicles — and certain types of people — it’s reassuring to know that we also have a vigilant ACLU keeping watch on the watchers. So far, those “certain types” are limited to missing persons, those on parole or probation or on the sex offender registry or the terror watch list. But this latest addition to the surveillance arsenal of the authorities could easily become much more intrusive, and therefore it seems to conjure up Big Brother for many people. Those who may automatically mistrust the American Civil Liberties Union for automatically mistrusting law enforcement agencies should consider that this may be exactly the kind of eternal vigilance that Ben Franklin urged us to maintain.Of course, you’re not supposed to be driving an unregistered or stolen vehicle, so that part is no grounds for complaint. But it’s not illegal to be on parole or probation, and it’s not illegal to be on those lists; it’s your actions that might call for the attention of the police, not your very existence.If used properly, the license plate scanner doesn’t seem to mark a tipping point that necessarily sends our society down the road to ruin; it’s just the newest weapon in the information arsenal of the local police. John Law and Uncle Sam have plenty of other ways to find out that which we used to consider private. It’s hard to imagine that this will come as news to anyone, but here are a few:• As we so memorably learned this year, the NSA has for quite a while been tracking “metadata” about phone calls made by reporters and other civilians in this country and internationally. We are told that all the agency recorded was what phone number called what other phone number, when, and for how long. We are told that the contents of the calls were not involved. Let’s hope so.• United States mail may still be considered sacred, even by Uncle Sam, but what about email? Most of us hardly think about how much we’re sharing that way, but we might if we knew that emails can be accessed by the authorities after 180 days.• Smartphones are almost ubiquitous today, but how many of us are aware that these devices are constantly reporting our GPS location to our carrier? And that government agencies including the NSA don’t seem to have much trouble getting telecom companies to pass that kind of data along?• People today seem entirely cavalier about sharing almost any kind of information over social networks such as Twitter and Facebook. Do they realize that law enforcement agencies believe that if you share information that way, you’ve already given up any expectation of privacy? Prospective employers often go to these sites to check up on people, so why shouldn’t the police?• Meanwhile, there are traffic cameras on highways and on more an more street corners, in cities and towns including Meriden; and even privately owned cameras on houses or at ATM locations can be accessed by law enforcement agencies.• And the FBI admits that it uses drones, “for surveillance,” in the United States.Add to all that the admittedly paranoid but not entirely unreasonable feeling that if “they” are spying on Tom and Dick, “they” are probably also spying on Harry, and you have a modern dilemma: We don’t know how much we’re being spied on, we don’t know who’s doing the spying and we don’t know how much they know. Worse, we’re pretty sure we’ll never find out.Plate scanning may be an acceptable police technique, in itself. What makes us nervous is that we have no idea what will come next — how long before every police department wants to have drones? There’s that, and the unsettling suspicion that wherever surveillance technology does lead, government will blindly follow.