It's one of Hulda Clark 's inventions. It is capable of detecting parasites and toxins in your body. You can see examples of it on YouTube (search for "syncrometer").
It is technically called an audio oscillator. It has this thing that you press that makes noise, and two plates. If you put a parasite or chemical on one plate, and leave the other empty it will tell you if you have the parasite or toxin in your body.
If you put, for example, a glass of water on one plate, and some arsenic on the other plate, then it will tell you if there's arsenic in the water.
The way it works is you press the noisemaker two times. If the sounds are the same, then the test is negative. If they are different then the test is positive.