Work at a pan in Etosha, Namibia has found that seismic sensors can be used to differentiate between elephant, giraffe, lion, gemsbok and human footfalls. The device known as the "geophone", was originally designed by the US military to detect enemy troop movements during the Vietnam War. It picks up displacement and converts it into voltage, and it is now used to collect vibrations caused by animals walking to a waterhole. Sound signatures are then analyzed to distinguish the different animals. The results show that the method worked well with differentiating elephants from other wildlife, with a success rate of 82 percent. However, counting elephant numbers using the geophones was only 55 percent accurate.The researchers are now attempting to make the military-designed sensors into an array to improve accuracy, reports Fiona Profitt of the BBC. The Stanford University researchers believe that the technique could be used to count forest elephants where aerial surveys do not work, i.e Central Africa. However, other scientists are doubtful that the high-tech technique can be practically applied.The frequent need to change batteries are among the key reasons why elephant ecologists are questioning the practicality of the device. Matt Walpole of Fauna and Flora International, said that the technique is impractical and cost prohibitive. "Given the detection radius is only 100m, you would need literally hundreds of them just to cover a few square kilometres," he said.The team believes that conservation management would improve by more accurate techniques for monitoring and estimating the size of elephant populations or other large mammals in Central Africa as these populations are relatively small and threatened by poaching.