Back in 2011, California discovered that the GPS anklets that track the movement of sex offenders and felons were not working as they were supposed to. The discovery came from a battery of tests that have, until now, been out of public view. The Los Angeles Times investigated a number of heavily censored court documents to piece together the story of how many of California's tagged felons were ineffectively monitored for months, leaving the public in "imminent danger." The documents show that in some cases, the tags were unable to correctly locate their wearers more than half of the time. The state has since changed providers, but as Ars Technica points out, reports of faulty GPS monitoring aren't limited to a single manufacturer.