If we can't reach you, we can't alert you! AlertOC is Orange County's mass emergency alert system and will rapidly send out messages when there is a perceived, emerging, or imminent situation that may require community action, such as evacuating your home. Yorba Linda residents are encouraged to sign up today at AlertOC.org. Please include your home address to ensure you receive the most relevant updates. Also, if you signed up for AlertOC in the past but have changed your phone number or home address, be sure to visit the website to update your profile and contact information.