A significant drop in barometric pressure typically means a storm is coming and you should take cover. When the storm alarm is active, Suunto 9 sounds an alarm and displays a storm symbol when the pressure drops 4 hPa (0.12 inHg) or more during a 3-hour period.
To activate the storm alarm:
When a storm alarm sounds, pressing any button ends the alarm. If no button is pressed, the alarm notification lasts for one minute. The storm symbol remains on the display until the weather conditions stabilize (pressure drop slows down).