What are testing tools in woodworking?

Woodworkers use tools that show the moisture content in a piece of wood. If a piece of wood has too much moisture in it, it could warp or crack after it had been used to make a piece of furniture, or whatever, and in effect, ruin the project.

Wood can also be tested for the presence of metal, such as an old nail that once held up a clothes line. Such a test could prevent the destruction of an expensive bit or blade, or a power tool from kicking back, (called kickback), which poses a danger to the woodworker.