When the sensor and app are in range, the FreeStyle Libre 2 system automatically communicates to give you Low and High sugar Alarms if they are turned on. The Low sugar Alarm notifies you if your sugar drops below the level you set. The alarm does not include your sugar reading, so you need to scan your sensor to check your sugar. The High sugar Alarm notifies you if your sugar rises above the level you set. The alarm does not include your sugar reading, so you need to scan your sensor to check your sugar reading.