  The main features of SG-WAS (SkyGlow Wireless Autonomous Sensor), a low-cost
device for measuring Night Sky Brightness (NSB), are presented. SG-WAS is based
on the TSL237 sensor --like the Unihedron Sky Quality Meter (SQM) or the
STARS4ALL Telescope Encoder and Sky Sensor (TESS)--, with wireless
communication (LoRa, WiFi, or LTE-M) and solar-powered rechargeable batteries.
Field tests have been performed on its autonomy, proving that it can go up to
20 days without direct solar irradiance and remain hibernating after that for
at least \mbox{4 months}, returning to operation once re-illuminated. A new
approach to the acquisition of average NSB measurements and their instrumental
uncertainty (of the order of thousandths of a magnitude) is presented. In
addition, the results of a new Sky Integrating Sphere (SIS) method have shown
the possibility of performing mass device calibration with uncertainties below
0.02 mag/arcsec$^2$. SG-WAS is the first fully autonomous and wireless low-cost
NSB sensor to be used as an independent or networked device in remote locations
without any additional infrastructure.
