The S12 is a complete telephone headset solution for those looking for hands-free convenience with clean, uncluttered design. S12 is the DuoSet™ with Firefly™ in-use indicator headset and a stylish adapter which connects to your telephone.

The Firefly™ in-use indicator headset is unique to Plantronics and features a bright LED that flashes when you are using the headset to make a telephone call. It is prominently situated near the headset microphone to ensure your colleagues are aware that you are using the telephone.
The headset features two wearing styles – a conformable earloop and an adjustable headband, with a behind-the-head
neckband as an optional extra.

The S12 adapter connects to your telephone. The adapter includes features such as headset/handset switch, volume control and mute control for your listening comfort. The adapter can either be powered using batteries or by an optional power supply unit.

The S12 is compatible with the majority of corded business telephones through the use of a slide switch and microphone level controls.

DuoSet convertible headset - choose your preferred wearing-style.
Firefly™ in-use indicator lets others know you are on the phone.
Noise-cancelling microphone allows your voice to be heard clearly.
Works with the majority of corded business telephones.
Volume adjustment to control your listening comfort.
Mute button for privacy when conferring with colleagues.
Hands -free-working.
Increased productivity.
Superior comfort.
Excellent call clarity.

More information:
Plantronics S12 Headset System (PDF)