he AS3935 works by detecting radio frequency emissions generated by lightning activity, and uses algorithms to distinguish these from man-made “disturbers” and to calculate the energy from strikes. From which it's able to then estimate the distance to the head of the storm over a 1–40km range.
The manufacturers, AMS, say that the AS3935 can be used “to protect both humans and equipment from harm by providing early warning of impending danger.” Suggesting that potential applications include use in hiking, at marine and sporting events, and with telecoms equipment, uninterruptible power supplies (UPS) and power conditioners etc.