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A jigger is an electronic countermeasures device on a Raptor.
Boomer tells Captain Lee Adama that her Raptor (now inside the cargo bay of Colonial One) is out of jiggers as well as other tactical tools such as communication drones (TRS: "Miniseries").
In her falsified description of her "return" to Caprica to retrieve the stranded Helo, Caprica-Valerii tells Helo that she "set the jiggers to pulse", suggesting that jiggers aid in masking a Raptor's electronic or DRADIS signature to enemy forces.
The Raptor that this Valerii had supposedly flown to the area is found surrounded by Cylon Centurions, making its use to return to Galactica impossible (TRS: "Water").