A method for detecting a pipeline pig traveling within a pipeline (P), the method comprising: sensing, by way of a passive pipeline pig signal detector , a series of impulses within a selected section of the pipeline having a frequency different than that of a signature frequency of the selected section of the pipeline, characterized in that the series of impulses are in an axial direction and caused by changes in momentum of the pipeline pig as it continually accelerates and decelerates during its travel between adjacent sources of vibration within the selected section of the pipeline due to changes in the frictional forces between the pipeline pig and the selected section of the pipeline, the adjacent sources of vibration being vibration sources selected from the group consisting of pipeline pumps, motors, and compressors; pipeline product and pipeline product flow; pipeline valves; pipeline weld seams; pipeline pig launchers and receivers; and pipeline reducers; the pipeline pig decelerating as the frictional forces increase and accelerating as the frictional forces decrease, a differential fluid pressure behind the pipeline pig increasing as the frictional forces increase and decreasing as the frictional forces decrease, each change in the momentum causing an impulse in the axial direction of the series of impulses; the passive pipeline pig signal detector comprises: a housing ; non-intrusive means for connecting the housing to an exterior wall of the pipeline, wherein no portion of the passive pipeline pig signal detector intrudes into an interior of the pipeline; at least one vibration sensor housed by the housing; and signal processing means including at least one band pass filter configured to receive at least a portion of the data collected by the at least one vibration sensor; the at least one vibration sensor and band pass filter configured to monitor the selected section of the pipeline and detect the series of impulses. sensing, by way of a passive pipeline pig signal detector , a series of impulses within a selected section of the pipeline having a frequency different than that of a signature frequency of the selected section of the pipeline, characterized in that the series of impulses are in an axial direction and caused by changes in momentum of the pipeline pig as it continually accelerates and decelerates during its travel between adjacent sources of vibration within the selected section of the pipeline due to changes in the frictional forces between the pipeline pig and the selected section of the pipeline, the adjacent sources of vibration being vibration sources selected from the group consisting of pipeline pumps, motors, and compressors; pipeline product and pipeline product flow; pipeline valves; pipeline weld seams; pipeline pig launchers and receivers; and pipeline reducers; the pipeline pig decelerating as the frictional forces increase and accelerating as the frictional forces decrease, a differential fluid pressure behind the pipeline pig increasing as the frictional forces increase and decreasing as the frictional forces decrease, each change in the momentum causing an impulse in the axial direction of the series of impulses; the passive pipeline pig signal detector comprises: a housing ; non-intrusive means for connecting the housing to an exterior wall of the pipeline, wherein no portion of the passive pipeline pig signal detector intrudes into an interior of the pipeline; at least one vibration sensor housed by the housing; and signal processing means including at least one band pass filter configured to receive at least a portion of the data collected by the at least one vibration sensor; the at least one vibration sensor and band pass filter configured to monitor the selected section of the pipeline and detect the series of impulses. <EOS>