You're definitely not alone — intermittent silent alarms are a well-documented issue on iOS 26, especially on iPhone 16 models. Here are the most effective fixes:
1. Check "Attention Aware Features" — Go to Settings > Face ID & Passcode > turn off "Attention Aware Features." When this is on, your iPhone lowers alarm volume if it detects you're looking at the screen. If you pick up your phone half-asleep, the alarm may go quiet.
2. Check alarm volume vs. ringer volume — Alarm volume is tied to the Ringer & Alerts slider, NOT the side volume buttons. Go to Settings > Sounds & Haptics > Ringer & Alerts, and make sure it's turned up. The physical volume buttons only change media volume by default.
3. Check if "Change with Buttons" is off — In the same Sounds & Haptics menu, if "Change with Buttons" is off, turning the volume buttons down before bed won't affect alarms — but if it's ON, you may have accidentally lowered the ringer volume without realizing it.
4. Make sure the alarm sound is not set to "None" — Open Clock > Alarms > edit the alarm > Sound — confirm a ringtone is selected and not "None."
5. Restart your iPhone — A simple restart clears background processes that can sometimes interfere with alarm audio output.
6. Check for iOS update — Go to Settings > General > Software Update. There have been known alarm bugs in early iOS 26 builds that were patched in later point releases.
If none of these help after trying for a few days, go to Settings > General > Transfer or Reset iPhone > Reset > Reset All Settings — this resets audio and notification settings without deleting your data.