BOISE -- After an officer-involved shooting in the Boise foothills shook the community on Saturday, many people became scared for their safety in an area that is seemingly safe.

To help protect you in this kind of emergency, Ada County has a notification system in place called Code Red.

One viewer reached out to KTVB's Morgan Boydston on Facebook and said she was hiking in the foothills with her family and their dogs right before this shooting happened. She wanted to know :what kind of alert system is in place to protect people during incidents like this? We found out it's as easy as signing up online or downloading a mobile app.

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"That was a very, very scary situation and without the app I would have had no idea," one Boise resident who lives just blocks from where the shooting occurred, Jordan Rossman, said. "It was pretty scary. I locked both my doors."

A little after 12 p.m. on Saturday, Rossman received a text message that said, "Boise Police are actively searching for an armed wanted subject. Please avoid the Hulls Gulch trail system until further notice."

Her cell phone number is registered with both the Code Red mobile alert app and her home address is registered on the Code Red website.

"A lot of us like to believe that we're in a really safe community where no harm to be done to anybody," Rossman added.

The Boise police and Boise fire departments responded to the shooting in the foothills on Saturday. As it escalated, emergency response commanders determined they needed to tell people in the area.

"On Saturday we used Code Red because we were in the middle of an active situation," Boise Police Department spokeswoman Haley Wililams told KTVB, "We had a scene unfolding that we needed to secure, so this was one way to alert people to stay out of that area."

BPD notified Ada County dispatch, who then mapped out an area and sent alerts to every landline in the boundary in this picture below:

Courtesy: Patrick Orr, Ada County Sheriff's Office
Courtesy: Patrick Orr, Ada County Sheriff's Office

Cell phone numbers and emails registered to an address in the boundary were also notified.

"Code Red can be used to alert somebody of danger or notifying them that we need their help," Williams added. "It allows us to alert a large number of people in one specific area."

Information from Ada County Dispatch shows 3,861 phone calls were completed and 181 text messages were sent on Saturday.

But the key is you have to sign up for Code Red in order to get notified of emergencies near you or in your community. You have the option of registering multiple addresses on the website; for example, you can be notified of anything happening near your home and near your work.

The mobile app is different: when you download Code Red Mobile alert, it tracks your location through GPS. In settings, you have the option of selecting a personal warning radius of up to 25 miles.

"So it follows you where you are, you can select to get that Code Red alert wherever you are. So even if you lived in Meridian and you happen to be in the foothills that day, you would still get the alert. It's not based on your Meridian address," Wililams said.

Alerts can be sent to specific neighborhoods or an entire community during anything from flooding and fires, to missing or lost persons, or in this case, a wanted man.

"The fact they sent me that forewarning and it being so close to home, it was wonderful. It was everything I was hoping I would get out of the app," Rossman added. "It's a really great thing to have."

MORE: Code Red used to alert neighbors about police activity

There are two different ways you can opt in to Code Red with your cell phone; one, you can go online to the Ada County Sheriff's Office website, click on the Code Red link and sign up your cell phone number and/or email. As mentioned, you can also download the Code Red Mobile Alert application on your phone.

All landlines within the zone mapped out by law enforcement are automatically registered for a reverse 911 call.