This whitepaper discusses the evolution of pig signallers, focusing on the shift from intrusive to non-intrusive technology. Intrusive pig signallers, rely on mechanical components and can pose challenges for maintenance, often requiring interventions that carry operational and environmental risk. Non-intrusive pig signallers, including magnetic, ultrasonic and acoustic types, offer significant advantages. They are safer, environmentally friendly and simplify maintenance. The choice of technology should be tailored to specific pipeline conditions and pig types. Overall, non-intrusive signallers promise enhanced safety, reduced environmental impact and operational efficiency.