If its a neutral spirit or vodka type liquid, and you have enough to fill a sample jar ,like a graduated cylinder or greater, then what you need is an alcohometer and a thermometer. Just bob the alcohometer in the sample, and the liquid level at the top, will intersect with the number on the gauge, giving you the % alcohol by volume. Double that number if you want proof ,i.e. 40% ABV = 80 proof,
I know that this type of unit isnt specifically suited well for accurate ABV readings of heavier liquids such as brandys etc. I always use it for grain and vodka. Also, you need the tempature, because most alcometers are calibrated for measuring a sample at 20 degrees Celcius. Any sample at a plus or minus temp to the 20 degrees, will initially give you an inaccurate reading. but this can be adjusted by adding or subtracting %'s, subsequent to the tempature of the sample, above or below the alchometer calibration. ,in this case, 20 degrees,. I hope I explained this ok and wasn't too confusing. I think I confused myself.

They have them at Brewhaus. See http://www.brewhaus.com/Distillation-Equipment.asp. and scroll down.
If you are running a pure product, ,like 96%, get the 0-100. also, if you need a test cylinder, for the sample and the alchometer, make sure it is made of glass and not plastic or acrylic. Higher proof spirits tend to mess with the plastics. Either it will melt, or it will turn your Vodka and such cloudy. be safe and get the glass.
If these ,glass, arent available through brewhaus, just check the net. You'll come across them easily.

I always break stuff that is glass I have the plastic one from brewhaus and it is great!