Jack Harkness's handcuffs

Jack Harkness carried a set of handcuffs which were used to bind Blon Fel-Fotch Passameer-Day Slitheen, while in the skin suit of Margaret Blaine, to the Ninth Doctor as they went out for dinner in Cardiff. Were Blon to move more than ten feet away from the Doctor, she would have been zapped by ten thousand volts. Ultimately, the Doctor took the handcuffs off when an earthquake struck the city. (TV: Boom Town)