OverSight for macOS
OverSight is an app that monitors your mac's mic and webcam and provides a visual alert when the mic is activated, or whenever a process accesses the webcam.
OverSight constantly monitors your mac for malware such as OSX/Eleanor, OSX/Crisis, OSX/Mokes, and others. Yes your webcam's LED does turn on whenever the webcam starts up there has been research that has shown malware is able to piggyback into an existing session of apps such as FaceTime, Sykpe, Google Hangouts, etc. recording both audio and video without being detected.
Note from the dev's
As with any security tool, direct or proactive attempts to specifically bypass OverSight's protections will likely succeed. Moreover, the current version over OverSight utilizes user-mode APIs in order to monitor for audio and video events. Thus any malware that has a kernel-mode or rootkit component may be able to access the webcam and mic in an undetected manner.
This app is only compatible with macOS 10.10+
This is a first release and the dev's say there will be many improvements to it in the future.