There is no better way to learn science and electronics than building your own measurement tools. The MightyOhm Geiger Counter Kit comes with everything you need to build a Geiger counter to detect radiation around you. This 100% open source kit has a LED and piezo speaker, 1 x ATtiny2313 microcontroller as its brain, and serial data logging.
This Geiger counter works with SI-3BG, SI-1G, and SBM-20 tubes. This kit comes with laser cut acrylic case, all the electronic parts, and batteries for you to put it together right out of the box.