The OV-Watch is a $99 wristworn sensor that measures the salts in the wearer’s sweat to identify when she’s most fertile. From the product page:
Researchers in the late 50s and early 60s noted that numerous salts (chloride, sodium, potassium) in a woman’s sweat fluctuated in relation to the menstrual cycle. Chloride levels are low at the start of the menstrual cycle and peak three times during the cycle (see graph below). Using a patented biosensor, OV-Watch detects a baseline chloride ion level for each woman and then accurately predicts ovulation based on the timing of the first peak. The OV-Watch detects the chloride surge 3 days prior to the estrogen surge, 4 days prior to the LH surge and 5 days prior to ovulation, making it an earlier predictor of ovulation than any other chemical surge during the month. During the clinical trials for FDA approval with Dr. Arthur Haney at Duke University, approximately 3 out of 4 women received the full 5 day notice of ovulation while only 1 in 6 women were given more than 12 to 24 hours notice with urine tests or LH kits.
Link (via Gizmodo and Medgadget)