Comment Chose Wisely. (Score 1) 277
There are lots of caveats as most of these meters are for detecting contamination rather than dose rate.
The CDV -700 has a pretty thick window so not super sensitive. They are all pretty old so you would be wise to check it carefully before using.
To reliably detect small amounts of radiation contaminating food you will need to spend a fair bit of money on something more sensitive that most of the survivalist supply stores:
http://www.ludlums.com/index.php?page=shop.product_details&flypage=flypage_ludlum.tpl&product_id=300&category_id=115&keyword=3_with&option=com_virtuemart&Itemid=95
(they will also do calibration)
Eberline made very good instruments but I can't find them on the web as making them currently. They made also very good equivalent products. You may find a good used one of these.
Proper NIST traceable calibration may be worth your time the meters are generally calibrated for dose rate or energy from a standard Cesium-137 source Cobalt-60 is commonly used and they are both major fission products so they are good choices for the stated application):
One vendor near NY I found on web: http://biomedphysics.com/survey-meter-calibration-and-repair
The Reed College Reactor Facility might also do it. This will likely be the cheapest method (website quotes $50 per probe +shipping): http://reactor.reed.edu/metercal.html
As others have mentioned most smoke detectors use Americium which is an alpha emitter. You need a very thin window and large surface area probe to detect this reliably. These don't make great test sources.
If you can find an older colman style lantern mantle made of thorium (the newer "safer" ones do NOT have thorium) they make great test sources and will set off most Geiger counters and are really useful as you should check to make sure it's working with every use. The probes are delicate, the batteries die etc so if it's important check every time. Keep them in a plastic bag so they don't contaminate your detector!
Good Luck!