How to detect microphone usage on OS X?

Question

Is there a way to detect when the microphone of my Mac is in use? Similar to what Mikro Snitch does? Can this be done in Cocoa?

Answer 1

My previous answer no longer works and was rather brittle (it only applied to the internal device). This is a quick solution for PyObjC, which can be translated to Objective-C or Swift reasonably easily.

import AVFoundation
import CoreAudio
import struct

mic_ids = {
    mic.connectionID(): mic
    for mic in AVFoundation.AVCaptureDevice.devicesWithMediaType_(
        AVFoundation.AVMediaTypeAudio
    )
}

opa = CoreAudio.AudioObjectPropertyAddress(
    CoreAudio.kAudioDevicePropertyDeviceIsRunningSomewhere,
    CoreAudio.kAudioObjectPropertyScopeGlobal,
    CoreAudio.kAudioObjectPropertyElementMaster
)

for mic_id in mic_ids:
    response = CoreAudio.AudioObjectGetPropertyData(mic_id, opa, 0, [], 4, None)
    print('Mic', mic_ids[mic_id], 'active:', bool(struct.unpack('I', response[2])[0]))

Note that this script will work once through, but if your app does not have a run loop, as observed in this question, repeated calls to AudioObjectGetPropertyData will always return the same result.

Answer 2

Is there a way to detect when the microphone of my Mac is in use?

Simple answer - Yes, but it's not going to be easy!

Can this be done in Cocoa?

As the documentation states: -

The Cocoa application layer is primarily responsible for the appearance of apps and their responsiveness to user actions

So this doesn't cover the microphone and if it did, it would be too high level for what you want.

A detailed answer on how to do this is complex and too broad for Stack Overflow. However, to set you off in the right direction, you need to create an IOKit kernel extension driver (KEXT) and have a good understanding of the I/O Registry