
Copper T is a small T-shaped device which is inserted into the uterine wall (IUD). It releases mineral ions which have a detrimental effect on sperm motility and viability. Here chances of preventing pregnancy are 99.9%.
Copper T does not provide any physical barrier during intercourse. So it does not prevent any types of sexually transmitted disease.
Photo Credit Medical gallery of Blausen Medical, CC-BY 3.0