When a person's heart suddenly stops beating, CPR can sometimes save that person's life. But if someone goes into cardiac arrest on the street, CPR might not be an option if no one nearby knows how to do it.

Now, researchers hoping to fix this problem have developed a mobile app that alerts people who are trained in CPR when someone nearby needs their help. In a new study, the researchers report that the app did indeed increase the rates of CPR performed on people undergoing cardiac arrest by 14 percentage points, according to the study.

In the study, about 9,800 adults in Stockholm who were already trained in CPR provided their cell phone numbers and agreed to be on call to assist people nearby who were experiencing a cardiac arrest. If anyone called the country's emergency number and reported a suspected cardiac arrest, a mobile alert system was ready to be activated that would connect these volunteers with the people in need of help.