Linger keeps your Mac awake only while you're actually in front of it, and lets it sleep when you leave — using on-device face recognition.
Open Settings… from the menu:
macOS turns on the green indicator whenever any app uses the camera — it can't be hidden. Linger only checks during idle moments and keeps each check very short.
No. Frames are analyzed on your Mac in memory and immediately discarded. Only a numeric faceprint is stored locally; nothing is ever transmitted. See the Privacy Policy.
That happens before you enroll. Once you enroll your face, only you keep it awake.
Make sure you're in good, even light and facing the camera. Try Re-enroll from the menu, and/or lower Match strictness in Settings.
Linger needs a working camera. With the lid closed (clamshell) and no external camera, presence checks can't run.
Settings → Remove my face data. Uninstalling Linger also removes everything it stored locally.
Minimal. The camera stays off while you're actively using the Mac, and only takes a brief look during idle periods.