A fallout meter is a radiation-measuring device that could be used to assess the amount of radiation in the ambient environment in the aftermath of a nuclear war. The name of the meter is a reference to fallout, highly radioactive particles that would rain down over large areas of the United States, Europe, and/or Russia in the event of a full-scale nuclear war. In the immediate hours, days, and weeks after the explosions, these particles would emit enough radiation to kill anyone unfortunate enough to be out in the open unshielded. Unfortunately, since the end of the Cold War, most people place little priority on learning about the dangers of fallout, and will hence be entirely unprepared in the event of a nuclear war.
A particle detector used to measure ionizing radiation, a fallout meter is an ion chamber that measures the prevalence of radiation by measuring its effects on a charged gas chamber. When a particle of ionizing radiation strikes the particles in the chamber, it causes them to lose charge in a way that can be precisely measured. The term "fallout meter" indicates a radiation-measuring device calibrated to accurately measuring large amounts of radiation, as might be present in the aftermath of a nuclear attack, effectively in a way that a traditional Geiger counter, made for lower radiation intensity situations, would be incapable.
The most popular fallout meter on the market today is the CDV-715 (Civil Defense Geiger Counter), which can be purchased for the affordable price of about $20 US Dollars. This meter was rolled out in 1962, at the height of Cold War fear. Besides the CDV-715, another notable fallout meter is the Kearny Fallout Meter, a fallout meter designed by civil defense expert Cresson Kearny. This fallout meter can be constructed by anyone from common household materials, including a tin can and aluminum leaves. The instructions on how to build the Kearny Fallout Meter are freely available on the Internet, and suitable for printing in a newspaper in case of an emergency.
Besides shelter, water, and food, a fallout meter is an absolutely essential item for surviving a post-attack situation. Without a fallout meter, one can only guess at the ambient intensity of fallout radiation, and a quick trip outside a shelter might be enough to cause radiation sickness, which consists of profuse vomiting and nausea followed by a slow death. If you believe that the probability of a nuclear war during your lifetime is non-negligible, then investing in a fallout meter would be a good idea for you and your family.