The Callisto Pulse was a device that could disarm micro-explosives up to twenty feet away.
River Song offered the pulse to Dorium Maldovar in exchange for a vortex manipulator that she required to reach the Eleventh Doctor. Dorium needed the Pulse to disarm the micro-explosives River had put in the glass of wine he had just drunk. The Pulse was in the form of River's earring. (TV: The Pandorica Opens)