Apple’s T2 security chip has been added to the new MacBook Air. It’s also in newer MacBook Pro models. And it can stop malicious parties from eavesdropping on your microphone when the lid is closed (via TechCrunch).
T2 Security Chip
The T2 security chip holds the MacBook’s encryption keys, fingerprint data, and has secure boot features. It also controls the ambient sensor, the system management controller (SMC), image signal processor, Apple video encoder, audio controller, and enables “Hey Siri.”
And according to Apple’s new security guide [PDF] it automatically disconnects the microphone when you close the MacBook’s lid.
All Mac portables with the Apple T2 Security Chip feature a hardware disconnect that ensures that the microphone is disabled whenever the lid is closed. This disconnect is implemented in hardware alone, and therefore prevents any software, even with root or kernel privileges in macOS, and even the software on the T2 chip, from engaging the microphone when the lid is closed.