Have you ever been using a headset and had someone start speaking to you? Prevent interruptions or conversations from ruining your time on line. The Busy Light is a polite, noticeable way to let people know you're on the phone. A long cord allows you to place the light where it will get seen the most. Turns on and off with a simple, positive-click switch. For those phones that do not need to have the handset lifted to use the headset. Requires 2 "AA" alkaline batteries (included).