For decades, all that separated the U.S. from Mexico was barbed wire.

Now, after a massive infusion of cash from Congress, President Donald Trump’s administration is swiftly building what it has dubbed a “smart wall,” a combination of 30-foot-tall (9-meter-tall) steel fencing and an array of sophisticated technology like sensors, cameras and towers allowing Border Patrol to surveil the territory.

The wall is under heavy scrutiny for the billions of dollars being dedicated to it when border crossings are at their lowest in decades. Critics say the U.S. is militarizing the border as it increasingly deploys sophisticated surveillance technology to the area, impacting local communities.

“We are seeing a massive expansion of surveillance and surveillance technology across the borderlands,” said Ricky Garza, border policy counsel at the Southern Border Communities Coalition, an advocacy group. “The wall in all its forms is harmful to communities.”

Officials say the technology is complementary to the physical wall and frees up agents for other tasks.