A startling warning of a shelter-in-place issued for a fire in the hills above Saratoga was Santa Clara County’s inaugural use of a system that targets cell phones in a given area.

But rather than just being sent to people in the immediate area Monday, the alert was issued to people all over the county.

According to the county’s Office of Emergency Services, the first sheriff’s deputy to arrive at the Eden Fire — a slow-moving blaze that broke out near Mt. Eden Road and Orchard Meadow Drive shortly after 3 p.m. Monday — saw that steep terrain could hinder access for fire trucks.

He told his sergeant that a “shelter in place” alert was warranted for residents on Mt. Eden Road, “to keep people off the road and allow clear access for fire equipment arriving on the scene,” said OES spokeswoman Patty Eaton.

Officials decided that in addition to the AlertSCC notification — which sends messages to residents who subscribe to the service via home phones, mobiles, email as well as automated “reverse 911” calls to landlines — a new IPAWS system would be activated, which hits all mobile phones in a designated area based on proximity to a cell phone tower.

The plan was to send it to people in the immediate area near the fire but instead the “Emergency Alert System function was inadvertently selected, which reaches a very broad audience,” Eaton said.

That meant people heard a blaring alarm on their phones far from Saratoga. Commenters on social media said they got it in Palo Alto, Redwood City, and in East San Jose, where they didn’t get one for last week’s fire that burned two homes and caused evacuations.

“We regret the error,” said Eaton, “However we are very pleased with the overall effectiveness of the system’s capabilities.”

Eaton said they are “reviewing procedures and making appropriate modifications” to make alerts more specific in the future. While the county is responsible for alerting people in unincorporated areas, each jurisdiction involved in the system is responsible for activating its own alert. None of the other jurisdictions has used IPAWS since its rollout, Eaton said.

While the county has been authorized to use such technology for two years, it wasn’t adapted until April 1 because the county was in the process of changing to a new system. Since its rollout, 15 cities and agencies have been trained and authorized to send out such alerts, Eaton said.

Eaton said that while the system had been tested, Monday was the first time the county has issued an IPAWS alert in a live situation. Eaton said training has been ongoing since the new system was integrated on April 1.

“We can reassure residents that we’re refining the use of these systems,” Eaton said. “Our targeting will become more accurate. And to look on the bright side, we have this vital, incredible tool that will let people know what is happening if it’s in a local community or more widespread. People need this.”