Micro Sniff 4+

Another 1-star review seems to mistake the purpose of this app - it only actually 'does anything' when the microphone device is being used, which is exactly the goal. I feel the need to correct it because this app is admirably open-sourced by its maker, meaning it's far more safe to use than most!

The overlay shows up nicely for me as expected whenever I open a tab in Chrome that utilizes my microphone.

I'd love to see an option to also detect camera usage and show a different overlay for that. I care more about camera detection than microphone detection.

Have you ever wondered if your microphone was secretly being used by one of your apps? Well, this app reveals the truth on that and it does it well. A neat popup is revealed on screen anytime that your microphone is in use, allowing for easy identification of any snoopers that try to spy on your conversations. In addition, this app is open-source and collects no data, allowing for peace of mind in knowing that this app is not secretly snooping on you for itself.

Whenever the microphone is in use, a small unobtrusive indicator appears on the screen.
The indicator remains on top, gently flashes, can be moved around as needed, and disappears when the microphone is no longer in use.
IMHO this increases security similar to the green LED camera in-use indicator.
An icon is also installs in the Menubar, and provides several preference settings.
Many thanks to the developer for writing this super handy little app.
PS. Made a minor suggestion to app developer. App developer replied quickly, and incorporated my suggestion. Awesome App, Awesome developer.