At least 115 people die every day in the U.S. after overdosing on opioids, according to the National Institute on Drug Abuse.
And in 2016, illegal injectable opioids became the most common drug involved in overdose-related deaths.
The team will publish its results Jan. 9 in Science Translational Medicine.
"The idea is that people can use the app during opioid use so that if they overdose, the phone can potentially connect them to a friend or emergency services to provide naloxone," said co-corresponding author Shyam Gollakota, an associate professor in the UW's Paul G. Allen School of Computer Science & Engineering.
"Here we show that we have created an algorithm for a smartphone that is capable of detecting overdoses by monitoring how someone's breathing changes before and after opioid use."
The Second Chance app sends inaudible sound waves from the phone to people's chests and then monitors the way the sound waves return to the phone to look for specific breathing patterns.