Related Clues:

• "Heads up!" and the like
• They might range from green to red
• Smartphone conveniences
• Messages to mailing-list members
• Traffic app notifications
• Civil defense sirens, e.g
• Some iPhone notifications
• Brings up to speed
• Phone beeps
• 'Duck!' and 'Timber!'
• Gives a warning to
• Smartphone notifications
• Notices on a cell, e.g
• Warnings of changes with temperature dropping
• Alarms, warning signals