ARGH! Toys and more toys!
Be aware that the ex-cold war meters are designed to detect and measure the fallout from nuclear bombs, this is somewhat hotter than natural background radiation. They might not be sensitive enough, see text of the PDRM 82. The PDRM 82 is a bit of well made, tough as old boots, kit.
The Smartphone plugin looks intriguing but the blurb isn't that convincing about background radiation.