Digital alerts sent Friday to San Luis Obispo county residents from the local Office of Emergency Services turned out to be false alarms, officials said.

The mobile phone warnings were sent out Friday afternoon and alerted people to a civil emergency for which everyone needed to "prepare to take action." The messaging mishap was accidentally triggered when Pacific Gas & Electric Co. workers updated the siren system at Diablo Canyon, a local nuclear power plant. The siren went off, and workers had to physically cut the power to stop the system.

"We thought sending out the message to them would be simple enough," county emergency services manager Ron Alsop said. "Unbeknownst to us, when we do that with our new digital emergency alert system, the new cellphone notification system also sent out [pre-scripted] cellphone alerts to residents."

Residents quickly became confused and worried. Nisse Noble, 27, was unsettled most by the message's lack of information. She told The Associated Press the vague alert made her worry about a mass shooting or a criminal at large in the area.

"We didn't know where we should turn or what we should prepare for," Noble said.

A follow-up alert informed everyone about the false alarm and said there was no need for concern. However, tweets from San Luis Obispo citizens continued to flood in, and some residents seemed upset about the unnecessary worry. One tweet from @dillondean read, "the accidental emergency alert made me scream. Someone is getting fired."

PG&E has been doing repairs and updates as part of a summerlong facility upgrade. This system also alerts people to other disasters and dangerous situations, such as dam failure or Amber Alerts. San Luis Obispo has had the system for only about a year, according to Aslop.

"The county certainly apologizes for this, although we are glad to know [the alerts go] out so quickly," Alsop said. "But we apologize for the disruption of people's days and any concern it caused."