The duders over at cookinghacks put together an Arduino based geiger counter. It's set up to click a speaker at every pulse for an immediate indication of radioactivity.

The Arduino and touchscreen are rather standard fare [Toumal] picked up on eBay for about $30. What really sets this project apart from all the other geiger counter builds we’ve seen is the ...

Watching the geiger counter rate against time and compairing to the background level seems a good way to go. Measuring the radiation level in a volume of captured rain water is also good idea.

GEIGER COUNTER: – 450V Power Supply – Arduino-driven Geiger Interface – 2x Dual SBM-20 Soviet-era Geiger Tubes – 16×2 i2c LCD – 5V to 9V DC-DC supply ...