do you have a list of components?

Hello Adam, 

Could you detect radon with your device?

Sorry for the late reply - I never got a notification about your message.

I don't think this device could be used to detect radon for a couple reasons. The geiger tube I used (STS-5) is mostly sensitive to high energy gamma and beta radiation, not alpha radiation which is what radon produces. Alpha radiation is also unable to penetrate the metal casing of my device. 

Another issue with the sensitivity of the geiger tube I use is that the count rate from background radiation is about 20 counts per minute. If you were to put the device in a higher radiation field giving 30 counts per minute, it would be hard to notice the difference just by ear. This device is better for directly measuring stronger radiation sources. 

Of course, this circuit could be used with a superior geiger tube in which case you could measure weaker fields more accurately.