Apple’s new T2 chip prevents hackers and malicious applications from eavesdropping on your conversations. New hardware feature physically disconnects the MacBook’s built-in microphone whenever the user closes the lid. The new chip is already present in the 2018 MacBook Pro models launched earlier this year. The chip also offers some non-security features as well, like an image signal processor that enables enhanced tone mapping, controls the ambient sensor, the system management controller (SMC), white balancing to the FaceTime HD camera, and enables “Hey Siri”
Source: https://thehackernews.com/2018/10/apple-macbook-microphone.html