The "electronic ankle bracelet" or "electronic shackle," which looks like an oversized wristwatch, sits above the ankle. It is supposed to offer the public better protection against offenders who have just been released from prison. For the past year, a team of 15 police officers and social workers from Bad Vilbel, Hesse, has supervised people around the clock who, despite having completed a prison term, are still considered a danger to the public. There are currently 31 former prisoners around Germany – a sentence of at least three years is a prerequisite for a court order to wear an ankle bracelet upon release.

"Electronic shackle" is a misleading term because the wearer can still move freely. Only the location of the wearer is recorded continuously using GPS. And if the person wearing it or someone tries to remove the tag, an alarm is triggered immediately – the same happens when the wearer enters an area that is prohibited by the court. That could be a kindergarten or school for child sex offenders.

When that happens, the central monitoring service calls the offender on his mobile phone, informs him that he has triggered the alarm and urges him to leave the restricted area immediately. And, if necessary, the local police are also informed – they can determine the location of the person and pursue him using GPS. Last year, ankle bracelets triggered such messages to the police 96 times.

Sexual abuse despite ankle bracelet

The bracelet cannot prevent crimes. In Munich, the trial of a man, who was previously convicted for sexual offenses, began in early January. He is accused of sexually abusing the daughter of his acquaintance at her home in April 2012, while he was wearing an electronic ankle bracelet.

"An electronic ankle bracelet will not stop a potential sex offender in any way from reoffending. Technology cannot prevent crime," Bernhard Witthaut, the chairman of the German Police Officers' Union, told DW.

Even though he doesn't want to ban ankle bracelets completely, Witthaut believes that their possible use is very limited.

Monitoring stalkers

However, the ankle bracelet made it easier to solve the case in Munich, says Christian Pfeiffer, the Director of the Criminological Research Institute of Lower Saxony.

"It helps the police gain access and it is a deterrent for most criminals. Sex offenders or drunks are not, of course, stopped by an ankle bracelet. Nevertheless, it's the right approach," adds Pfeiffer, who also served as Lower Saxony's attorney general.

Studies in the US demonstrate the unique deterrent effect of the ankle bracelet, he notes.

It has also been used to protect against stalkers – a receiver automatically alerts the person who is being stalked that the stalker is in the vicinity. Using ankle bracelets in Germany would make sense, Pfeiffer says. He advocated this during his time as attorney general, but was unsuccessful.

Still, the relatively low financial investment would make sense for politicians, he says.

"The ankle bracelet costs 230 euros ($310) per month. Imprisoning criminals costs 130 euros – per day," Witthaut notes.

But the bracelets should not be used as an alternative to imprisonment or surveillance by on-site police officers, he says, adding that they could be used to monitor compliance with court orders at best.