Smart Pig 

In-line inspection is a technique used to assess the integrity of natural gas transmission pipelines from the inside of the pipe and is used by SoCalGas as part of its ongoing pipeline integrity program. In-line inspection involves the use of technologically advanced equipment, often referred to as "smart pigs" or in-line inspection tools, which are deployed inside the pipeline. Smart pigs were originally named for the squealing sound they make while travelling through a pipeline. Originally, pigs were used to clean out debris and remove water from a line after a hydro test. Now, they are more commonly used to carry sophisticated technology that can internally inspect a pipeline for anomalies.