Ovulation Kits test how much LH (Luteinizing hormone) is in your urine. This is helpful since the amount of LH increases 1 - 2 days before ovulation. So, it is a marker that ovulation is soon to occur.

There are some really expensive ones that over a hundred dollars and some that are pretty cheap for a few dollars. The cheap ones work fine, but the more expensive one has a digital read and alerts you to your most fertile days. (Thought the cost is high, it is nothing compared to the cost of the kid!) When you buy the expensive one though, you are not done... you still have to buy strips for it, and they aren't cheap either.