Ovulation predictor kits (OPKs) are tools used to help individuals identify their fertile window during the menstrual cycle. These kits typically measure the levels of luteinizing hormone (LH) in urine, which surges just before ovulation. By detecting this surge, users can better time intercourse for conception. OPKs come in various forms, including test strips and digital devices. To use an OPK, a person usually tests their urine daily during the days leading up to ovulation. This method can be particularly helpful for those trying to conceive, as it increases the chances of successful fertilization.