OPKs mostly measure Lh (lutenizing hormone) the hormone that surges immediately before ovulation to shove that eggy outta there. It is normally detectable in urine 12-48 hours before ovulation. This is that magic window we're shooting (pun intended) at with IUI/ICI. The problem is when you are shipping frozen sperm in a 22lb tank from California to Texas, you need more than 12 hours notice. ALSO, sometimes the Lh surge isn't detectable, or is easy to miss, in which case you miss ovulation and wait ANOTHER MONTH to do it all over again. Most sperm banks will guarantee the quality of the sperm out of the bank, in the tank for no more than 7 days. (That was a Dr. Suess moment, no?) Some of them only five. So basically, counting a day or two shipping each way, you have to hit it pretty dang close to have them on hand for possible ovulation, and still be able to get them back to the bank if you don't end up using them. Remember, we're talking about $2,000 worth sperm flying around here.
The OvaCue fertility monitor measure Lh in your saliva. Evidently Lh shows up first in saliva, then your blood, and finally urine. SO the Ovacue can give you a "Peak Day" estimation five to seven days ahead of time *and the crowd goes wild*! This is priceless information for folks in my situation, and helps SO much in scheduling/shipping/medicating etc. You put the sensor on your tongue for five seconds first thing every morning, before eating, drinking and brushing your teeth, and it magically (in my humble opinion) gives you your reading. You can also purchase it's magic accessory (which actually *does* look like a magic wand) the Vaginal Sensor to confirm ovulation after the fact. While that part might seem inconsequential, since it is *after the fact* it's actually priceless. The sensor gives you an idea of how your ovulation symptoms correlate to ACTUAL ovulation AND let's you know after an insemination how good your timing was.
Below is an example of my current-ish (August) OvaCue screen. As the blue days get darker, I'm getting closer to my "peak" day of estimated ovulation. August the 10th was my darkest peak day, and then it turned pink because I got ovulation confirmation that night. You can also see that it has already estimated my fertile period for September, but those dates will most likely adjust with more readings, and as it gets closer. I can see how it would be SUPER helpful to couples conceiving the old fashioned way (notice I didn't say "normal") and with an endless supply of sperm, but it is especially helpful for those of us that are having our swimmers flown in, and having to be so specific on timing. I've had ovulation confirmation on my "peak" day every cycle so far! I'm IMPRESSED!