Radiation can kill -- so can buying the wrong "Geiger Counter" ! Many of the sellers on eBay are selling the yellow Civil Defense radiation monitors as "Geiger counters" when they are NOT true Geiger counters. Simply put, for a device to be called a Geiger counter it must use a Geiger-Mueller tube as its radiation detector. Only the CDV 700 unit uses a Geiger tube, housed in the detachable chrome wand or "hot-dog" probe. A vast majority of the surplus Civil Defense units being sold as Geiger counters are actually Ion Chamber devices which are designed to only register lethal or near-lethal doses of radiation. These "fallout meters" include the CDV units numbered above 700 (i.e. the CDV 710, 715, 717, 720, etc.). Fallout meters were designed to measure the massive doses of radioactivity present in and around a recent nuclear blast, and were used to tell how much time a person could spend in the blast zone without becoming seriously ill or fatally irradiated. They were not designed to detect the small amounts of radiation present in such common household items as Vaseline Glass, Radium painted watch hands and other self-luminescent "glow-in-the-dark" items, Thoriated welding rods, antiques (including quack medical devices), and naturally radioactive ore / rock specimens. An Ion Chamber device will not tell you if an item is slightly radioactive, it only registers ionizing fields that are thousands of times stronger than those emitted by these common items. Because of this, one should only use a true Geiger counter to check for small doses of radioactivity. If your CDV Ion Chamber unit actually begins to show significant movement of the meter needle -- RUN !!! Survivalists should be aware that these two different types of instruments were designed for two different jobs. In a fallout situation the radiation may be strong enough to "saturate" a true Geiger counter, overwhelming its ability to measure the high number of counts generated in a strong radioactive field and causing it to give no reading at all when in fact there is plenty of radiation present. However, to check food, water, or other items for contamination only a true Geiger counter can measure the small amounts of radioactivity that may be present. Make sure you pick the proper tool for the job !