There are two ways that a notification can be displayed on your iPhone when the device is unlocked. One is ‘Banners’ and the other is ‘Alerts’. In the ‘Banners’ setting, the notification will appear on the top of the screen and disappear after a brief interval (about 10 seconds).
Due to this, the alarm will also stop ringing when the notification disappears. In the ‘Alerts’ setting, the notification will appear in the middle of the screen and required user intervention to remove the notification. In this case, the alarm will ring for the complete 30 seconds.
So, if you want the alarms to ring for the whole 30 seconds duration when your device is unlocked, then please do the following:
1. Open ‘Settings’ app.
2. Browse to ‘Notifications > Galarm’.
3. Select the ‘Alert Style When Unlocked’ as ‘Alerts’.