If you lived in London, or were visiting there, you would be subject to at least 500 thousand cameras discreetly posted on many street corners in that huge city. Every day, photos of you and your companions would enter an archive of countless other pictures, available for the police and other authorities to consult.

Much closer to hand, I have just discovered to my amazement that the MBTA uses surveillance cameras at each of its stations to record images of all riders passing through fare gates. These images are routinely saved for 30 days and monitored by transit system police. Whether other people are aware of this practice I do not know. In any event, the public seems to have accepted it as a matter of course.

Also your telephone company keeps an electronic record of every call you make and every call you receive. Your private conversations are thus available to anyone entitled, or perhaps not entitled, to tap into them.

And the credit cards you use provide not just a record of an individual transaction but other information about you as well. Your credit record, and a profile of your habits as a consumer, can easily be drawn from the data inscribed on your card.

Similarly, Radio Frequency Identification tags can be implanted in a product and recognize who you are. These silicon chips are able to identify you when you approach a given site: a gas pump perhaps or a store entrance.

These facts I report, not to alarm you, but to highlight how much the world in which we live has changed in a remarkably short time. As with other changes, those worked by electronics go far beyond what we ever anticipated or even now may be aware of.

My own awareness has been raised by a new book Blown To Bits, written by a friend, Harry Lewis, in collaboration with Hal Abelson and Ken Ledeen. The three authors are experts in computer science who understand how digital technology has transformed contemporary reality.

Some features of this revolution give cause for concern, even alarm. They have infringed on privacy so as to make conduct you consider your own business the potential business of everybody else.

But they have also brought new ways to assure safety and security. The authors begin their book by citing the story of a Seattle woman who lost control of her car and remained for days lost in its wreckage, mired in a ravine. Her whereabouts were finally discovered when her cell phone records revealed her exact location.

Ironically, she would not have been found had her husband not become a suspect in her disappearance. That suspicion allowed the police to examine her cell phone record that otherwise would have remained off limits to them.

Another of the myriad benefits of the digital revolution allows computer users easily to obtain information about virtually everything. By using a search engine such as Google or Yahoo, you can find out almost anything you want to know.

Though most of the time we remain unaware of it, information technology routinely records events in our daily life. My car, for example, has a transponder on the windshield that allows me to pass through toll booths without stopping to pay cash. Not only the Massachusetts Turnpike but major roads in other states automatically charge my account every time I pass through.

These transponders provide the state with detailed information about locations but they can also take note of the speed at which we drive.

In addition to a transponder, my Toyota probably has an “event data recorder” that saves information such as speed, braking time, turn signals, and other facts that would be useful in the investigation of an accident.

Of course, the ability to write and receive email adds a dimension to daily living previously undreamed of by my generation. However, this benefit, too, brings hazards along with its perks.

What interests me, as usual, is the differences of outlook among generations. Younger people appear to accept these phenomena without wonder or alarm. As Harry Lewis has said: “Young people assume that’s the way the world should work.” After all, if they are below a certain age, they have never known anything else.

But I judge it important for them to know the problems that come with the digital explosion. As noted, privacy remains a chief issue, unlikely to be resolved any time soon. Similarly, free speech faces threats that can endanger our democracy. It has become easier for governments, and indeed other institutions, to control thought.

As with so much else in the modern world, the reality is mixed. Lewis says that the coauthors had exciting experiences while writing the book. “We ourselves kept on having ‘holy cow’ moments,” he says. That’s because the new technology packs so much punch, along with pressing questions for all of us.

Richard Griffin