The readings on this page were obtained using one of the Black Cat Systems radiation detectors.
The detector is connected to an ordinary computer (Windows or Macintosh) running a copy of the Rad software and connected to the internet (dialup, cable modem, dsl, etc). Rad automatically sends the current radiation reading to the web server that hosts this site, which generates the map showing the readings for all radiation monitoring stations. Rad is included free with any of our radiation detectors.
Source: Black Cat Systems