  I first read about this in Sarah Blaffer Hrdy's Mother Nature, and I thought then, if this is true, it would be fantastic to have! I've finally gotten around to finding it. By spitting into this test kit, which fits in your purse or wherever, you can look for non-fertile vs. fertile shaped spit bubbles. Apparently, it's pretty obvious. It predicts ovulating days up to 72 hours in advance. Since I'm absolutely BC pill non-compatible (it turns me into an unpleasant person, to say the least), and my old method of the cervical cap isn't so reliable after babies, I'm already dependent on natural family planning methods. And this is a huge advance in that area. Conversely, if you're aiming for those fertile days, this would also be a big help. urlLink OvuLook Saliva Ovulation Tester 
