Hi Lynny,
You can buy a little device which is a microscope with which you look at your saliva. When your saliva has lots of oestrogen in it, which it does at your peak fertile time, then it shows up as a pattern just like fern fronds.
It is quite amazing - I used one for the first time this month. I usually use OPKs because I don't always gets lots of CM. this month I got an +ve OPK at 6pm one day, then had lots of CM, the next afternoon, then got the ferning that evening (about 24 hours after I got the +OPK). It gives a better indication of when you might be O'ing as an OPK just tells you when you are about to 0.