TapNoiseA dark display is not enough evidence that your Mac requires authentication. Lock the screen explicitly when stepping away, and check the password delay that applies after the screen saver or display sleep.
Use an explicit lock
Control-Command-Q locks the current session. Save important work first, since someone with physical access can still shut down or restart the computer.
The lock screen protects access to your session. It does not anchor the Mac to the desk or provide a location history.
Review the idle delay
Open System Settings › Lock Screen and inspect Require password after screen saver begins or display is turned off. Choose a delay that matches your security needs and verify it with a harmless test.
Display-off timing and password timing are related settings with different jobs. A screen can go dark before the password requirement you intended takes effect.
Keep extra controls in perspective
TapNoise can send the screen-lock shortcut through a configured knock action on supported MacBooks with the required permission. Test it in advance and confirm the lock screen actually appears.
Guard Mode adds an alarm with its own limits; it is not a substitute for locking the session. For locating a missing machine, Find My versus a software alarm explains the separate recovery role.
Sources: Apple’s password-after-wake guide, TapNoise knock controls.