[jamii]

A nice intermediate step is to attach a small light directly to the mic/camera, so that the light is on whenever they are being used.

[joshzayin]

They already do this for the camera, though I'm not sure if it's hardware or software.

[sounds]

It's firmware, loaded on boot and replaceable by someone with root permissions.

So it's not a trivial thing to bypass, but it's not secure. Use a sticker or post-it note if you're paranoid.

[jaylevitt]

Are you sure? A day or two ago someone on HN said that newer MacBooks had the LED wired in series with the camera's power supply.