Japan-based Sanwa has announced the so-called Geiger Fukushima [JP], a portable and light (70g) geiger counter that uses the iPhone to measure beta and gamma rays in your environment. Just connect the 14cm long probe to the iPhone, fire up an app that supports the device and view the handset’s display to track radiation readings.
There are many portable geiger counters out there, but the idea here is to make use of the iPhone’s capabilities to keep the price down: just the handset and the Geiger Fukushima are enough. The device can be ordered by people living outside Japan, too (it costs US$203 in the Japan Trend Shop).
Sanwa says the measuring range for the Geiger Fukushima stands at 0.04-20 microsieverts per hour and that one AAA battery lasts about 200 hours.