Police in Hawaii will ticket people who get caught looking at digital devices while crossing a street in the state capital, Honolulu.
The law, passed in July, came into effect this week, making Honolulu the first major city in the U.S. to pass such a law.
The only exemption to the Distracted Walking Law is to use a device to call 911 to report an emergency.
The fines for the offenses will range from $15 to up to $99 for repeat offenders.
Pedestrians are still allowed to talk on their phones while crossing the streets, as long as they look at their surroundings.
The National Safety Council added "distracted walking" to its annual list of injury risks in 2015.
According to a study in the Journal of Safety Studies in 2015, some 400 pedestrians distracted by a phone were injured in the United States each year between the years 2000 and 2007. But after the introduction of the smartphone, the numbers have risen. The study found an estimated 1,300 pedestrians were injured in 2012.