The V-700 is a government issue Geiger counter stockpiled during the 1960’s for Civil Defense use in the event of nuclear war, and now available to you and me for $20 to $80 from surplus suppliers and auction sites such as eBay.
Built like a tank, most of them are still in great shape 40 years later, and set an example that should be met by more tool manufacturers. The Geiger counter reads gamma and beta radiation, with a probe shield to discriminate between the two. It includes a check-source on the side of the can for instant testing, runs off standard flashlight D-cells, and comes with a carry strap, earphone, and manual. The manual (while short) covers use, calibration, maintenance, emergency/MacGyver repairs, and has full schematics and parts list. The schematic is also reproduced inside the case, which is water tight, and EMP resistant.
While most people have limited (if any) genuine need for a geiger counter, they are interesting devices, and are useful for a variety of purposes — from aids in learning about natural background radiation and geology (while hiking?), to adding radiation survival equipment to an emergency kit. Radiation detection equipment, being too niche to really feel market forces, has evolved surprisingly little in the last 40 years, so most of the difference between one of my $20 V-700s and one of my $800 modern meters is bells and whistles, and more reliable calibration systems.
However, since these are sometimes over 40 years old, and there are many differing models and manufacturers, a little buyer savvy is needed: Most, but not all are still in working condition, so avoid “untested, as is” if you need it to work out of the box. Many are sold with accessories missing (eg no manual or earphone), but any missing manuals can be found online in pdf format at Southern Radiation.
(Note: These manuals are also useful for researching a particular model of v-700 before you buy).
A quick rundown on the models: Do not buy a V-717, V-720, or V-715 – these are ion chamber survey meters, not Geiger counters. They are designed to complement the v-700 in times of nuclear war – their needle only starts to move when the Geiger counter is off the scale (so you’ll need a radiation lab just to test if they even work). If emergency gear is your purpose, one of these might be on the list after a v-700. They are cheaper than a v-700, but a lab test will likely be $60.
For the v-700, I recommend the Victoreen model 6A or 6B, because it has a depleted uranium check-source with millions of years half-life, so the “level” of the check-source remains constant. The Lionel 6B has a more elegant circuit that only requires two batteries instead of four, but the check-source often has a half-life of as little as 6 years, so calculations must be made to compensate when calibrating. The Anton models I would avoid – they are older, in my experience much less reliable, and have the short half-life check-sources. The Anton model 5 is worth a mention though if space is a consideration because it is smaller than the rest. The Electro-Neutronics Inc (ENI) are apparently good, but I do not own any, so have no experience.