Objective-See:

OverSight monitors a mac’s mic and webcam, alerting the user when the internal mic is activated, or whenever a process accesses the webcam.

OverSight constantly monitors a system, alerting a user whenever the internal microphone is activated, or the built-in webcam is accessed. And yes, while the webcam’s LED will turn on whenever a session is initially started, new research has shown that malware can surreptitious piggyback into such existing sessions (FaceTime, Sykpe, Google Hangouts, etc.) and record both audio and video – without fear of detection.

It’s free and offers a little peace of mind for the paranoid among us.