Cry Baby #6
Overview
The Cry baby is an electronic device that essentially simulates the distress call of a large (usually Union of Allied Planets) ship, making a fine distraction when there is a need to make a Tohoku-class cruiser decide between chasing your ship or rescuing what they think is a big ship full of people. It is highly illegal for any of a dozen reasons.
History
Serenity's crew uses such a device inside a Blue Sun Corporation coffee can (Cry baby #6) to good effect in the Firefly's pilot episode "Serenity", and later on the motion picture Serenity.