The safety LED on a 6-way extension socket (such as smart-protect or surge-protected A-06/ECSP06 models) indicates that the internal protection circuitry, grounding, and power-supply connection are actively functioning. When lit, it confirms your devices are guarded against voltage spikes. If it turns off, the surge protection component may have worn out or sacrificed itself to block a power spike. [1, 2, 3, 4, 5]