Condom

A condom was a piece of plastic material used during sex to prevent pregnancy. Lauren Anderson's roommate left one for her. (HOMEVID: Zygon: When Being You Just Isn't Enough)

Jack Harkness insisted on using condoms when having sex with Brad, given the recent return of his mortality due to Miracle Day. Though Brad initially objected that they "don't need nothing in between", he relented after Jack said, "Lifetime of regret just got even longer." (TV: Dead of Night)