Some iPhone users report alarms triggering silently because the sound setting was reset to 'None'. This appears to affect a small number of devices, potentially linked to older alarms using 'Classic' tones. Checking the Clock app for each alarm's sound setting is the immediate fix.

The glitch's cause remains unclear, but it highlights how iOS settings can occasionally reset. For reliable wake-ups, ensure the alarm volume in Settings > Sounds & Haptics is fixed, not tied to physical buttons. Also, verify Sleep alarms have a dedicated sound and disable Face ID attention-aware features that can lower volume if the phone detects a face.

This issue underscores the importance of manually testing critical functions like alarms. While not widespread, it's a frustrating bug for those affected. Apple has not yet commented on a permanent software fix, so users should periodically verify their alarm configurations to avoid missing important commitments.