Made by DKL International in Vienna, VA, LifeGuard can scan buildings, vehicles, or other areas where direct observation of humans is prevented or dangerous. The range adjustment device (RAD) on the LifeGuard's snout resembles an antenna; however, instead of receiving an electromagnetic signal, it detects the edge of an electric field. To operate it, a user holds the grip and aims the RAD toward the area to be scanned and then moves it in a sweeping motion. The device travels freely when no electric field is detected, but the user feels a resistant drag on the device when a human electric field is encountered. Electricity produced by the heart of living animals produces an electric field detected by LifeGuard, these electrical impulses of less than 30 cycles per second travel through barriers that absorb or reflect higher frequency energy. LifeGuard designers matched the device to a human's electric field. It is equipped with an SPF filter that differentiates between humans and other living creatures or inanimate objects with electrical fields. The design is based on the fact that the human electric field is unique. LifeGuard can scan a 180-degree arch out to 400-500 meters. If a human is detected within that range, a narrower bearing can be obtained. Double-blind testing has produced a 96-percent accuracy rate.