"Wire cutters" is the phrase exchanged between Linh Cinder and Emperor Kaito as a warning of bioelectrical manipulation. Cinder vowed to never bioelectrically manipulate Kai without warning, so, on the Rampion, the pair came up with the code words "wire cutters."
The name originated when Cinder was repairing the Rampion, and she asked Kai to hand over the wire cutters.
The phrase was used several times throughout the fourth book. One notable occasion was when the Rampion crew were pretending to be American diplomats whose ship had broken down. Lihn Cinder announced, "this could have been avoided if someone had remembered to bring the wire cutters," and Kai knew it was her.