Trumpet player for the 43-year-old New York Philharmonic, Christopher Martin lost his alliance while playing baseball in Central Park. With the help of Ring Finders, he was paired with Jeronimo Barerra, who showed up at the park with two metal detectors, one for each of them. After about an hour of digging and no sign of the ring, Martin was ready to give up. Barerra's persistence paid off: when a family that was organizing a picnic cleaned up and left, he swept his detector and heard a beep, it was Martin's ringtone.

Martin and Rodriguez are not the lucky few who have been able to recover their lost jewels. Metal detectives have surprisingly managed to find missing rings. Barrera, 45, vice president of the video game company behind the viral success Grand Theft Auto, has recovered 20 of the 30 rings he has been instructed to locate. All ring researchers have agreed that if the person knows roughly where the item was last seen, it will probably be discovered. As Barrera has said, the success rate is "close to 90% for those where calls are directed to a specific location in Central Park, or to the beach or a construction site", compared to more blurry locations such than somewhere in the center of Manhattan.

Metal detectors cover the entire age and background range, but like Barrera, they are mostly men. "The members are 90% male, 10% female, but that changes," said Turner.

One of the reasons why metal detectors have such a good reputation is that, through practice, they have fine-tuned their strategy to find rings. "If I can not find them, I'm not sure they're where they think they are," says Mike Fish, a ring hunter living in Anchorage, Alaska. The retired 71-year-old firefighter is asking for a small fee: chocolate chip cookies.

"It's a lot of work," says Steve Smith, a retired 63-year-old welder based in Rancho Palos Verdes, California. "People do not understand. You find a lot of trash before finding a treasure. He says he has found about 50% of the 500 or so rings he has been looking for. Sometimes, he spends hours searching for a ring just for the customer to realize that it's in a pocket or at home from the beginning.

The process of finding a ring begins with determining exactly where it was lost. Like all metal detectives tell me, most of their customers without rings are wrong on the scene, sometimes a little, often a lot. "They are never where people think they are. They are 30, 60 or 100 yards away, "said Turner.

Smith explained how the process worked afterwards. "Once I basically read the ringtone from the questions I'm asking, we organize a meeting in their yard, at the beach or at the park. They take me to the area and we rediscover how they lost their ring, in what direction they were, what happened right now. A bit like a detective, I look for a starting point for my research, taking care to cover the whole area, because if you had missed it, you missed it by far.