Confirm suspicions of infidelity of a spouse or significant other, Determine if minor children are engaging in sexual intercourse Collect evidence that may prove signs of sexual child molestation. Semen Detection Spy Kit uses an extremely accurate testing method called PSA (Prostate Specific Antigen). PSA is one of the major proteins found in seminal fluid and it can also be found in the absence of spermatozoa in the case of men whom have had a vasectomy. Scientists have been able to recover PSA from semen stains as old as 30 years!