“Six months doesn’t sound so bad. I mean, compared to the guys I’ve met who were in for five years or fifteen years, I had it good. But it’s still plenty long enough to lose your job. Lose your family. Even lose your friends, people you thought you could rely on. Seemed like more than enough punishment for carrying some weed.”

In 2014, Ralph Turner, a 25-year-old truck driver and father of two, was arrested in San Jose on suspicion of possessing marijuana. Turner had been carrying over 30 grams, and after a short trial he was convicted and given a mandatory sentence of six months in prison.

California’s prisons were full to bursting, and with the state in the midst of a severe and extended budget crisis, it couldn’t afford to build any more. Faced with no alternatives, the court enrolled Ralph Turner into a pilot probation programme aimed at low risk offenders.

Turner was taken to an induction centre and shown a short video, and then his cell number was entered into a computer. A technician looped a measuring tape around Turner’s ankle and after a short wait, snapped a light plastic ring into place. He was free to go, and inadvertently became one of the first people to benefit from America’s slow turn away from its ruinously expensive and ineffective penal system.

The object I’m holding right now, an ‘ankle monitor’, is a thin ring of plastic, maybe half a centimeter thick if you count the inner padding. Inside the plastic is a simple computer, a radio, and a microphone array.

Like earlier monitors, it can locate the wearer by satellite positioning and send a warning if they’re leaving or approaching restricted areas. But Turner’s monitor is a little different: its microphone array constantly records and streams every nearby sound to a remote server, so if the wearer is suspected of violating their probation, the relevant audio section can be decrypted by court order. More controversially, in a concession to public fears, the monitor doesn’t just relay its position to the police and judicial system, it also informs a whole range of ‘concerned parties’ including schools, hospitals, and airports.

The theory was that this new generation of ankle monitors could be used for non-violent low risk offenders, such as those convicted of drugs possession or petty theft or vandalism. Not only would they save tens of thousands of dollars per person, they’d also allow the wearers to continue their jobs and live with their families. Coupled with mandatory community service, the monitors seemed to be the best — and only — alternative to a penal system that was too expensive and that barely appeared to reduce crime at all. Expert Amira Goss elaborates:

“Over ten million people worldwide were imprisoned in 2014, and a full quarter of them lived in America, a country with only 5% of the world’s population. Incredibly, most Americans gave little thought to their system of incarceration and if anything, many felt it was too lenient. The fact that prisons only became commonplace as a means of punishment in the 19th century was completely overlooked.

“From a historical perspective, America’s penal system was little different from the old ‘debtors’ prisons’, with many inmates made to work at below minimum wage to pay their way. Not only was it incredibly wasteful, but worse still, it didn’t really work. Recidivism rates were stubbornly high, and even long sentences didn’t seem to deter criminals who had few other options in life. My view is that they became more about retribution, and the very literal removal of criminals from sight — an understandable impulse for severe crimes like murder, but not for petty theft.”

In the years between 1970 and 2014, US incarceration rates increased five-fold thanks to mandatory sentencing laws, privatisation of the prison system, and much stricter attitudes to crime and punishment compared to other rich countries. The human cost of putting close to one in a hundred adults in jail was horrific, and certainly not worth the relatively modest decrease in crime rates, assuming that there was even any causal link.

Prison had become a place that destroyed families and jobs and bred a virulent criminal culture. As befitting the time, though, it wasn’t the human cost that eventually caused the change in direction which led to our ankle monitor; it was the economic cost. By the early 21st century, keeping someone in jail cost almost as much as the average US income.

The new ankle monitors were met with fierce resistance in California from all points along the political spectrum. The ACLU argued that the ankle tags violated human rights on a massive scale, while state Republicans claimed that ‘freeing’ tens of thousands of prisoners would cause a violent crime wave. As revealed by data miners taking advantage of transparency laws enacted in the 50s, much of the opposition was funded by donations from corporations profiting from private prisons, but at the time their warnings were met by a frightened and receptive public.

The government had little choice, though; it simply couldn’t afford the expense of housing so many prisoners. Thanks to a powerful speech from Reverend James Malone, a charismatic religious leader, the public was eventually convinced that it was better to try and reintegrate prisoners with society rather than lose a fortune on them.

The problems began almost immediately. Ankle monitors or not, many wearers weren’t dissuaded from committing crimes, even though they were swiftly apprehended. Hundreds more wearers simply vanished, and troublingly, several wearers were unfairly punished for simple malfunctions of their monitors.

As predicted by security experts, monitors were reverse-engineered in order to spoof and intercept the tracking signals. A firmware update eventually addressed these issues, but for a while, it was possible for anyone with the right equipment to track the wearers. Most damningly, the audio recordings were usually too poor in quality to be useful as evidence, at least until new hardware was released in 2018 and integrated with the wearers’ other sensors.

Yet the government forged on. Too much had been invested to give up now, and the promise of massive savings dazzled their judgement. Three years on, the pilot programme was expanded to all low-risk offenders and taken up by several other cash-strapped states convinced that it was an easy way to save money; in New York and Pennsylvania, the monitors were linked into a flexible community service system that allowed a much wider set of institutions — churches, charities, businesses — to work with offenders through automatic reporting and wireless tracking.

In the vanguard states, sentences became shorter, swifter, and surer. By 2036, the prison population in the US had been cut by a third, saving tens of billions a year — and more importantly, helping millions of offenders stay in work and keep their families intact.

What fascinates us today about ankle monitors is how they represent the dilemmas and compromises that were typical of the early 21st century. It would be a mistake to attribute the sweeping change in the US penal system to a mere piece of technology rather than its human backers and designers, but they still remain a powerful symbol. Social historian Julie Yao observes:

“The monitors were important because they helped to break a spiral of alienation and failure among prisoners. It’s easy for us to think that the Americans of 2014 were somehow heartless, but the truth is that most genuinely believed that prison was the only thing that stopped people from committing crimes, thanks to the sensationalist media.

“Monitors brought punishment and rehabilitation back into the open — but at the massive cost of normalising ubiquitous surveillance, a decision that we all know had serious consequences later in the century.”

We can’t know what Turner was thinking during his six months of monitored probation with his ankle monitor, but inspection of his nascent casters including Facebook, IMs, and text messages shows that he seemed to fare well enough. In an interview years later, Turner remarked, “I didn’t enjoy being a guinea pig one bit, and I sure as hell didn’t appreciate someone being able to listen in on everything that I did. But if you gave me the choice between prison and the monitor, you’re damn right I’d have strapped that thing on my ankle with my own two hands.”

Follow me at @adrianhon and @futureobjects

A History of the Future in 100 Objects will be available on Kindle, iPhone and iPad this summer as an eBook and iOS Newsstand app. A lovely coffee-table book will be out this autumn.