# Introduction

The Safecast bGeigie Nano is a portable radiation sensor with GPS designed for citizen radiation monitoring (car, bike, on foot etc.). It records dose rate values along with appropriate date/time and GPS coordinates every 5 seconds and writes it on built-in microSD card.

bGeigie Nano is equipped with a pancake Geiger-Müller tube. A recorded number of pulses per time interval is automatically converted to the dose rate. The calculation is based on a device calibration, using Cs-137 source and a resulting physical variable. A resulting physical variable is called for simplicity just “dose rate”, although in actual truth it is “ambient dose equivalent rate” (ADER) to be measured in microSv/h (microSievert per hour).

The current Safecast solution contains bGeigie portable devices and online services to process the measurements and display them in an interactive map. However, as in many cases a reliable internet connection is not available. An offline solution is required, not only for monitoring in distant areas, but also for possible use of bGeigies to provide supporting data for crisis management in case of radiation accident.