Their idea was to help teenagers struggling with the feeling that life wasn't worth living.
Charlie, 13, and his sister, Hannah, 16, are the brains, and hearts, behind the new app "notOK," which sends a message to a handful of trusted friends, along with the user's GPS location, with the touch of a button.
Hannah was diagnosed last year with a heart condition called postural orthostatic taciecardious syndrome (POTS), which means her blood pressure and blood volume are extremely low.
"So when I stand up or sit up, the blood pools in my legs and in my feet and makes me pass out," she told InsideEdition.com Monday.
She was terrified of being alone, fearing she would lose consciousness with no one to help her. She fell into a morass of depression and took to holing up in her room and cutting herself.
"So my mom walked in on me one night, when I was self-harming, and she said, 'Hannah, why?' And so she held me, and in the midst of all that chaos, I wished there was an app... that I could press and send out a notification to my closest three to five friends and say, 'Hey, Hannah Lucas is not OK, come find her.'''
And after months of planning and designing, that's just what she and her brother did.
She's already used the app at school to summon her mother after fainting spells. More than 6,000 people have downloaded the app at a cost of $2.99 a month.
"It just makes me feel great that I actually helped her, and now I just won't find her in her room, cutting," said Charlie.
Hannah feels pretty good herself.
"I feel like there is a burden lifted off my chest and off my shoulders, now that I am able to be, live more freely now," she said.
Their mother shares those emotions, but admits she was skeptical when her son and daughter laid out their app plans.
"Oh yeah, I’m speechless you know, it’s like they did it, they actually did it. They said they were going to do it and I didn’t believe them," said Robin.
The young entrepreneurs are proud of what they've done. They're also passionate about wanting to help others who may be having a hard time finding a reason to believe.
"It just makes me feel awesome, like, 'Hey, I thought I couldn’t help her, but now I can. Now I can actually make a difference in other people’s [lives]," said Charlie. "It’s just been awesome so far."