STORY: Earlier this year, a secretive group of activists in South Korea quietly released a so-called 'smart balloon' into the night sky, with a course charted over the border into reclusive North Korea.

It carried a sophisticated, 15-pound payload.

When the group launches them, they may include mechanical leaflet dispensers, bundles of speakers, or GPS trackers.

The activist group has been developing these intricate devices since 2016, with regular launches since 2022.

The group has not previously discussed its activities with the media.

Once or twice a month from spring to fall, when the wind blows north, they launch the balloons with an aim to go deeper into the North, dropping thousands of leaflets and blasting recordings critical of Supreme Leader Kim Jong Un in a North Korean accent.

This one is saying, "Kim Jong Un is a traitor that opposes the people and reunification."

Balloon warfare between activists like these - and the North - took center stage late last month, when Pyongyang sent more than 1,000 balloons south- most filled with garbage and, reportedly, manure.

Pyongyang officials said these were retaliation for a propaganda campaign by North Korean defectors and activists in South Korea.

The Seoul-based activist group that flies the 'smart balloons' is among these groups - its known as "The Committee for Reform and Opening up of Joson".

Joson is often used as another name for North Korea.

The group was founded by a North Korean defector and now has around 30 core members.

They declined to be identified not only over worries they may face harassment from South Koreans critical of balloon activism, but also crackdowns from authorities or even reprisals by North Korean agents.

This member said North Korea's recent behavior was seen as a sign the group's tactics are working.

"Kim Yo Jong recently said South Korea should experience how unpleasant, how tiring it is to clean up their trash balloons and this means North Korea is admitting that our smart balloons were scattered over large parts of their country."

In a small rented apartment in Seoul, the team uses 3D printers to build white plastic boxes and components.

Most balloons contain devices pre-programmed to scatter 1,500 leaflets, 25 at a time, depending on flying conditions.

"The smart balloons can scatter leaflets over a very large area, from an area as small as 30 miles and as wide as 180."

Filled with hydrogen, the group's smart balloons stretch nearly 40 feet in length.

Typical cargo might be six speakers to blast audio and six additional bundles, each containing a bible and a short-wave radio.

The group recently added altimeter-linked valves that prevent the balloons from going too high, which makes for a more stable flight.

They estimate their balloons have a 50-60% success rate of going further than a dozen miles or so north of the border, with batteries that last for days.

One cleared North Korea entirely, making it all the way to China.

The flights are controversial in South Korea, with some residents arguing the balloons are confrontational and put them at risk.

And with no way to independently verify where they land or what average North Koreans might think about the contents, it's a debate as to how effective they are.

Despite all that, "The Committee" said they have no plans to dial back their operation any time soon.

"This should never be stopped for the sake of the North Korean people and their freedom and rights by delivering information on freedom."