CAMBRIDGE, ENGLAND—Archaeologist Christos Tsirogiannis of Cambridge University is concerned about the popularity of metal detecting as a hobby—there are an estimated 10,000 enthusiasts and in 2011, they uncovered close to one million artifacts. “I’m sure that there are several people who are operating metal detectors and they do it just for excitement. But even in a legal way, the destruction that they generate is really big, and it is an unfortunate phenomenon that it is still legal,” he says. Those who trespass in their search for precious artifacts under the cover of darkness are known as “nighthawks.” Yet archaeologist Suzie Thomas thinks that metal detector hobbyists who record their finds can be a great help to scientists. “The sub-discipline of battle archaeology makes a lot of use of metal detected data because they’re looking at objects like cannon balls and musket balls that are, of course, metal. Having the data of where on the field they’ve been found can help you reconstruct how the battle went, and that’s incredibly useful information,” she counters.