The Stones Have Ears

he US military is “developing miniature electronic sensors disguised as rocks that can be dropped from an aircraft and used to help detect the sound of approaching enemy combatants.The devices, which would be no larger than a golf ball, could be ready for use in about 18 months. They use tiny silicon chips and radio frequency identification (RFID) technology that is so sensitive that it can detect the sound of a human footfall at 20ft to 30ft. The project is being carried out by scientists at North Dakota State University, which has licensed nano-technology processes from Alien Technology, a California-based commercial manufacturer of RFID tags for supermarkets. [...] The new sensors would be made cheaply enough to be left on the ground without need for retrieval by soldiers. RFID technology uses radio signals that are sent from a silicon chip to a remote sensing device.”