This product is either discontinued or we cannot get that from suppliers.
Poly Plantronics Ring Detector 78887-01, Rd-1 - Shoretel / Toshiba, Black, 3.5mm port.
This product sends a ring alert signal to your headset when the phone is ringing anywhere within a headset’s wireless range. This product is designed for use with phones that also support native “load detect” (LD) headset hook switch (EHS) control.