South Korean middle school students use their smartphones today in Seoul, South Korea. The app, “Smart Sheriff,” was funded by the government to block access to pornography and other offensive content online.

SEOUL, South Korea — Lee Chang-june can be miles from his 12-year-old son but still know when he plays a smartphone game. With the press of an app he can see his son’s phone activity, disable apps or totally shut down the smartphone.

The app, “Smart Sheriff,” was funded by the South Korean government primarily to block access to pornography and other offensive content online. But its features go well beyond that.

Smart Sheriff and at least 14 other apps allow parents to monitor how long their children use their smartphones, how many times they use apps and which websites they visit. Some send a child’s location data to parents and issue an alert when a child searches keywords such as “suicide,” “pregnancy” and “bully” or receives messages with those words.

In South Korea, the apps have been downloaded at least 480,000 times.

The number will likely go up. Last month, South Korea’s Korea Communications Commission, which has sweeping powers covering the telecommunications industry, required telecoms companies and parents to ensure Smart Sheriff or one of the other monitoring apps is installed when anyone 18 or younger gets a new smartphone. The measure doesn’t apply to old smartphones but most schools sent out letters to parents encouraging them to install the software anyway.

Many countries have safety filtering tools for the Internet but it is rare to enforce them by law. Japan enacted a law in 2009 but unlike South Korea it allows parents to opt out.

South Korea’s new system is by no means impervious. For one, it can only be fully applied to Android phones not Apple phones. But cybersecurity experts and Internet advocacy groups argue the monitoring infringes too far on privacy and free speech. Some warn it will produce a generation inured to intrusive surveillance.

“It is the same as installing a surveillance camera in teenagers’ smartphones,” said Kim Kha Yeun, a general counsel at Open Net Korea, a nonprofit organization that is appealing the regulator’s ordinance. “We are going to raise people who are accustomed to surveillance.”

Many Koreans get their first smartphone when they are young. Eight out of 10 South Koreans 18 and younger own a smartphone, according to data. Some 72 percent of elementary school students owned a smartphone in 2013, a jump from 20 percent in 2011.

How technology is affecting the young has become a national obsession. The government and parent groups have pushed numerous initiatives to limit device and Internet use as well as prevent excessive gaming. Many parents welcome the ability to peer inside their children’s online world.

Lee, who worked in the online game industry for nearly a decade, said having a control over his son’s smartphone has been positive and increased dialogue in the family. His son plays a mobile game about two hours on weekends. If he wants to play a mobile game outside those hours, he comes up to dad and talks about why.

“What is important is that parents and children talk to each other and try to build consensus. He is only in a sixth grade but he wants to have his privacy,” Lee said. “I told him: We are installing this and father will know which app you use. I see it as positive in helping nurture his habit of self-control.”