Get a second hand (army surplus is a good source) Geiger counter with an instrumentation output. You may have to do some conversion if your current computer does not do RS232.
A release from NK or Russia, by the time it hits your Geiger counter, will likely be so low that it will be lost in the noise of background radiation. And local sources (such as radon gas) would mask anything but significant nearby events.
The reason why France identified the release is because their detectors can determine different radioisotopes.
It's a little like the difference between a photovoltaic cell and a camera. Your Geiger counter can tell when the "light's on" (presence of radiation) but it takes a different instrument to determine that it's Ruthenium 106.
You're much more likely to get an increase in background going into your basement (because of Radon daughters) than from an nuclear release halfway around the planet.