This is the Plantronics S12 replacement/spare headset. This Headset comes with a "firefly" in-use busy light at tip of microphone. This headset plugs directly into Plantronics S12 base with modular (square) plug. This headset is the replacement for your existing S12 system only. It will NOT work with any other Plantronics amplifier.
Important Note: This S12 replacement Headset comes only with the ear hook (not with the over-the-head headband attachment or ear cushions, sold separately). See picture.