The Extech EMF510 measures energy from electromagnetic fields (EMF) and electrical signals and is sensitive to extremely low frequency levels (ELF). The built-in single-axis sensor is ideal for monitoring power lines, electrical appliances, fans and blowers, and electrical circuits in two ranges with milli-Gauss and micro-Tesla units. The EMF510 features a large backlit LCD for viewing in dimly lit areas, an ergonomic compact design with wrist strap, auto power off, and Min/Max function. Complete with wrist strap and 3 AAA batteries.