() Under President Trump’s administration, military troops aren’t just watching the border.

Usually in the background in armored vehicles, using long-range cameras, now they are resorting to sound systems to warn migrants before they attempt to cross. And in Nogales, Ariz., thousands of troops have been deployed to National Defense Areas, militarized zones where the U.S. military and Border Patrol operate side by side.

“So, this is the LRAD, which stands for Long Range Acoustic Device,” Sgt. Ernesto Nevarez explained. “It basically broadcasts any tone or any voice at a longer distance.”

Thus far, the Army’s presence in Nogales is impossible to miss, with 117 armored vehicles, more than 35 helicopters, and high-tech surveillance gear, including drones scanning the skies. However, the troops have their way to send a clear warning sounding the alarm.

“Then we can inform them with this,” Nevarez added.

“And we can inform them that if they cross over the barrier, they will be in our national defense area. That is an early warning. If they cross into our national defense area, then they will be detained.”

While border crossings are down nationally, Arizona is still seeing significant numbers. Just last week, 135 people were charged with immigration-related crimes, including 67 for illegal re-entry, 13 for human smuggling, and five for assaulting federal officers.

Some suspects were wanted for violent crimes in Mexico. Others attacked federal officers during arrest attempts.

And with cartels changing tactics, this mission keeps expanding across Arizona’s toughest terrain.

“For us at least, we’re just watching. So, we’re not affecting anyone in any way,” Army Sgt. Ana Harker said.

“But if things get to be different, where there is a crime or something that’s happening, we also have eyes on us where we can also say stop, and we can get BP (Border Patrol) to get there and stop that crime.”

Arizona isn’t the only state that was added to the National Defense Area list. A few weeks ago, the Rio Grande Valley in South Texas was also added to the mission.