When you use the CLA 7, you can also speak directly to your caller by the microphone inside the system. So, the device works as a wireless system. Compatible with our products: Ampli DECT, CL200, 400, 500 & with most cellular phones (you may need to purchase a connector if your mobile does not have a suitable headset socket). Don.t forget to switch your hearing aid to T mode. Note: OFF:LEDisoffON:LEDisgreenLowbattery:LEDisredLoopON/OFFbuttonMicrophoneON/OFF&lowbatteriesindicatorLevelknobadjustme