The uRADMonitor KIT1.1 is an Open Source Digital Radiation Dosimeter, that can be used both as a portable detector, but also as a monitoring station to upload readings to the uRADMonitor network. It relies on a Geiger tube to detect radiation. This can be build by anyone interested with minimum effort.
Construction details are available on the project’s page, while the PCB files and the firmware source code are also hosted on Github, released under GPL v2. The code is hosted both on Google code and Github, all those interested are welcome to contribute.