Unlike most of ExacuTrack’s clientele, of course, I wore my device by choice and only briefly, to find out how it felt and how people reacted to it. By contrast, a real sex offender—or any of a variety of other lawbreakers, including killers, check bouncers, thieves, and drug users—might wear the unit or one like it for years, or even decades. He (and the offender is generally a “he”) would wear it all day and all night, into the shower and under the sheets—perhaps with an AC adapter cord snaking out into a wall socket for charging. The device would enable the monitoring company to follow his every move, from home to work to the store, and, in consultation with a parole or probation officer, to keep him away from kindergartens, playgrounds, Jonas Brothers concerts, and other places where kids congregate. Should he decide to snip off the anklet (the band is rubber, and would succumb easily to pruning shears), a severed cable would alert the company that he had tampered with the unit, and absent a very good excuse he would likely be sent back to prison. Little wonder that the law-enforcement officer who installed my ExacuTrack noted that he was doing me a favor by unboxing a fresh unit: over their lifetimes, many of the trackers become encrusted with the filth and dead skin of previous bearers, some of whom are infected with prison plagues such as herpes or hepatitis. Officers clean the units and replace the straps between users, but I strongly preferred not to have anything rubbing against my ankle that had spent years rubbing against someone else’s.

Increasingly, GPS devices such as the one I wore are looking like an appealing alternative to conventional incarceration, as it becomes ever clearer that, in the United States at least, traditional prison has become more or less synonymous with failed prison. By almost any metric, our practice of locking large numbers of people behind bars has proved at best ineffective and at worst a national disgrace. According to a recent Pew report, 2.3 million Americans are currently incarcerated—enough people to fill the city of Houston. Since 1983, the number of inmates has more than tripled and the total cost of corrections has jumped sixfold, from $10.4 billion to $68.7 billion. In California, the cost per inmate has kept pace with the cost of an Ivy League education, at just shy of $50,000 a year.

This might make some sense if crime rates had also tripled. But they haven’t: rather, even as crime has fallen, the sentences served by criminals have grown, thanks in large part to mandatory minimums and draconian three-strikes rules—politically popular measures that have shown little deterrent effect but have left the prison system overflowing with inmates. The vogue for incarceration might also make sense if the prisons repaid society’s investment by releasing reformed inmates who behaved better than before they were locked up. But that isn’t the case either: half of those released are back in prison within three years. Indeed, research by the economists Jesse Shapiro of the University of Chicago and M. Keith Chen of Yale indicates that the stated purpose of incarceration, which is to place prisoners under harsh conditions on the assumption that they will be “scared straight,” is actively counterproductive. Such conditions—and U.S. prisons are astonishingly harsh, with as many as 20 percent of male inmates facing sexual assault—typically harden criminals, making them more violent and predatory. Essentially, when we lock someone up today, we are agreeing to pay a large (and growing) sum of money merely to put off dealing with him until he is released in a few years, often as a greater menace to society than when he went in.