If you set your iOS device to "Do Not Disturb”, alerts from all apps will be suppressed and you will not receive anything. iOS apps are not allowed to override Apple’s "Do Not Disturb” feature. This is a restriction that Apple places on app developers. Setting your device to vibrate will still allow you to receive alerts but you won't hear the three Storm Shield alert beeps if an important warning alert is received while on vibrate mode. If you wish to hear Storm Shield alerts, your device will need to be on ringer loud for best results.