The tropical forests of the Congo Basin are geographically vast, remote, and impossible to patrol for illegal bush-meat hunting, say the researchers. Park-ranger patrols in tropical Africa often rely on intelligence information from informants, which can be unreliable or outdated. Even if the information is accurate, the timing of missions and regions targeted by patrol units rarely intersects with poacher activity.

The problem, says Gulick, is that the parks are understaffed. The Nouabalé-Ndoki National Park, for example, covers an area of 400,000 hectares (roughly 1,500 square miles). Yet only about 15 rangers man the area, says Gulick. "The patrols are infrequent and random, and the probability of catching poachers is almost zero."

Because the vegetation is dense, both people and animals tend to traverse the parks via well-established trails. Gulick's metal detectors are designed to be buried in the ground along these trails. Two detectors buried about 100 meters apart reveal the direction in which the poachers are headed. To avoid false alarms, the detectors only respond to ferrous metals such as iron and steel. Aluminum tent poles, for example, wouldn't trigger a response. The sensitivity of the devices can also be fine-tuned so that items such as pocketknives slip by undetected. Rangers and other park personnel who need to carry rifles would carry a device that would signal their identity to the detectors.

Many other groups have also expressed an interest in using Gulick's system. James Gibbs, a conservation biologist at the State University of New York (SUNY) College of Environmental Science and Forestry, in Syracuse, thinks that TrailGuard could be a valuable tool for protecting the heavily poached snow leopard in the Altai region of Central Asia, as well as the giant tortoises that inhabit the Galapagos Islands.

"With vast tracts of wilderness, trapping poachers is like looking for a needle in a haystack," says Gibbs, who met Gulick while working in the Altai and invited him to SUNY as a visiting scholar. "But TrailGuard could improve the efficiency in the [park rangers'] response. There would be less poking around in the dark."

"I don't think it will solve all problems," Gibbs continues. "There may be issues with deployment, data collection, and ramping up the production [of the sensors]. But it could potentially change the nature of interactions with poachers."