Microphone.devices

Description

A list of available microphone devices, identified by name.

You can use the name with the Start and End functions to specify which microphone you wish to start/stop recording.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Start() {
        foreach (string device in Microphone.devices) {
            Debug.Log("Name: " + device);
        }
    }
}

See Also: Start, End, IsRecording.