WASHINGTON (REUTERS) - If you take opioids, make sure your smartphone is handy.

That's not a glib suggestion but a potential way to save your life, say researchers at the University of Washington in Seattle, who are developing an app they hope will eventually help prevent deadly drug overdoses.

Called Second Chance, it would work like this: A heroin or other drug user logs into the app before taking the drug. Sonar technology then monitors that person's breathing from a distance of up to 3 feet.

PHD student at the University of Washington's Paul G. Allen School of Computer Science and Engineering, Rajalakshmi Nandakumar said: "We send an inaudible sound signal using the smartphone speaker and this sound signal gets reflected off the person's body. So I'm in front of it, it's going to get reflected off me, off my chest."

If the person's breathing drops below seven breaths-per-minute, the app would then call 911, or a friend or family member with access to the life-saving drug Narcan - which reverses the symptoms of an opioid overdose.

Researchers tested the app in conjunction with North America's first supervised drug consumption site, InSite in Vancouver, Canada, after developing Second Chance within a hospital setting.

Said University of Washington medical centre anaesthesiologist Jacob Sunshine: "In the operating room here we give Fentanyl and other medications as indicated to patients, that can lead to the types of breathing that occur when people may experience an overdose outside of the hospital."

The United States has the highest per capita rate of opioid use in the world. More than 72,000 Americans died from drug overdoses in 2017.

The University of Washington is currently applying for U.S. Food and Drug Administration approval for the app.