Researchers at Syracuse University in New York have recently developed a system that can detect the presence of humans in a given environment by analyzing ambient radio frequency (RF) signals. This new system, presented in a paper pre-published on arXiv, employs a convolutional neural network (CNN) trained on a vast amount of RF data. "Initially, we tried to detect drones in an outdoor environment using passive RF signals through deep learning," Biao Chen, one of the researchers who carried out the study, told TechXplore. "The result was uneven at best--it worked on measurements collected on certain days, but would fail on other days." For some time, Chen and his colleagues tried to develop a system that could sense the presence of drones in outdoor environments.