Regardless of what “the wall” is made of or how much more of it is ever built, it will always be just one of many instruments in the toolbox of security measures on the U.S.-Mexico border.

Many devices, technologies and personnel work together to prevent drugs and people from illegally entering the United States.

Here are two common scenarios that require completely different tactics.

Sorting contraband from cargo at ports of entry

During “pre-inspection,” while a line of cars is waiting to cross, a alerts its handler to something inside a truck. The vehicle is flagged for secondary inspection.

A scans the truck and the image reveals a suspicious compartment in its bed.

An officer uses a handheld to confirm heroin residue. The driver is arrested.

The U.S.-Mexico border has 47 land ports of entry through which about a half-million commercial trucks, cars and pedestrians enter the United States every day. U.S. Customs and Border Protection officers have the difficult job of expediting traffic while keeping an eye out for illegal crossers and cargo. Everyone and everything undergoes a primary inspection, in which license plates are scanned and passports are checked against Homeland Security data, said Blas Nuñez-Neto, a researcher at Rand Corporation and former senior advisor to the CBP commissioner.

Detecting and tracking people in remote areas

In the middle of the night, a detects human footsteps in an area miles from the nearest Border Patrol station.

Agents in a control center check footage from in the area, spot a group of people and track them as they walk.

Other agents in an SUV head toward the area with mobile surveillance gear and to locate and apprehend the group.

Between ports of entry, Border Patrol agents may be stationed miles apart, so they depend on various types of electronic surveillance to detect and track suspicious activity until they get there. If people move out of surveillance range, agents use classic tracking methods such as following footprints from the last known location.

We wanted to know not just what is there but also the strengths and limitations, so we talked to two experts who provided some perspective: Nuñez-Neto, formerly of CBP, and Adam Isacson, who analyzes border security for the Washington Office on Latin America (WOLA).

Physical barriers (a.k.a. “the wall”)

PROS Delay would-be border crossers long enough for agents to catch them.

CONS Largely ineffective in remote areas; susceptible to vandalism; expensive to maintain; obvious and immovable, so people may simply go elsewhere.

About a third of the southern border, nearly 700 miles, is lined with some kind of wall or fence.

Imposing pedestrian barriers comprise about half of that and are most useful in densely populated areas where nearby law enforcement officers can apprehend people quickly. They are made of materials such as bollards, steel slats with mesh panels, fences topped with concertina wire — even rows of carbon steel Vietnam-era helicopter landing mats. Some areas have two or three rows of barriers separated by a Border Patrol road.

[Analysis: The history of U.S. border apprehensions]

The rest of the barriers are mostly low-slung vehicle barriers that stop cars and trucks but not people on foot. Sometimes barriers attempt to funnel people or vehicles to open places where agents can most easily intercept them.

In San Diego, a segment of wall stretches along the U.S. border with Tijuana, Mexico, at right. (Carolyn Van Houten/The Washington Post)

Cargo scanners

PROS Very effective; next-generation models will be able to scan vehicles in line before they arrive at a port of entry.

CONS Expensive; require extensive training; more are needed; some date from the early 2000s and need to be upgraded.

Most illegal drugs that come into the United States from Mexico are smuggled through ports of entry, often mixed among legitimate goods, hidden in secret compartments or even in vehicle’s gas tanks.

Large X-ray and gamma-ray scanners identify illicit substances or hidden people by looking for differences in the density of cargo, such as a recent truckload of cucumbers that also contained almost 650 pounds of fentanyl and methamphetamine under a false floor. These scanners are mounted next to traffic or on moveable trucks and peer into vehicles horizontally as they pass by. Radiation detection devices are also used.

Ground sensors

PROS Provides ears on the ground rather than just eyes.

CONS Many false alarms because calibrating them to tell a person from, say, a deer can be difficult; smugglers figure out where they are; no tech has reliably detected tunnels.

Buried seismic sensors, often paired with cameras, detect when a person (or animal, car or even a low-flying plane) is moving in the area, and the sensors ideally can differentiate among those things. The sensors ping border agents in a control center so they can take a look at camera footage of the area. Other aboveground sensors and ground-penetrating radar are used to find tunnels.


PROS Can stay aloft for weeks at a time; not thwarted by undulating terrain.

CONS Sidelined by bad weather; radar can’t penetrate thick foliage; expensive to operate; may raise privacy concerns; one once broke loose and wreaked havoc.

Six roughly 200-foot-long unmanned, blimplike aerostats float thousands of feet above key areas of the U.S.-Mexico border. Each carries a downward-pointing radar system that can detect vehicles within a 200-mile radius and send data through its tether to a control station on the ground.

Aerostats are particularly good at detecting low-flying aircraft, such as the ones drug smugglers use, because their radar isn’t blocked by hilly terrain the way ground-based radar can be. And newer, smaller versions fly closer to the ground and carry radar that can better identify people. But Nuñez-Neto said it’s no secret that aerostats can’t fly in bad weather, and “the smugglers can read the weather forecast just as well as we can.”

An aerostat used by the Air and Marine Operations division of U.S. Customs and Border Protection in Eagle Pass, Tex., in 2017. (U.S. Customs and Border Protection)


PROS Excellent image quality; Predators theoretically can stay in the air for 24 hours; small drones are portable, agile and quick to deploy.

CONS Expensive; require a lot of manpower; dependent on good weather; raise privacy concerns for nearby residents.

Since 2006, huge Predator B surveillance drones have patrolled the border from above 19,000 feet, capturing and transmitting live video and detailed infrared and radar images of people on the ground. More recently deployed smaller drones produce even better images, which reportedly are sharp enough to identify a person’s height, weight and hairstyle.

Like aerostats, however, drones can’t fly in bad weather.

Fixed surveillance towers

PROS Most effective in flat, wide-open areas.

CONS Radar can be blocked by hilly and leafy terrain; very visible, so people can see and try to avoid them; require people to monitor the feeds.

“Integrated Fixed Towers” as they are officially called look like TV station towers that soar to 160 feet high. Each is equipped with radar, high-resolution daytime cameras and infrared cameras to monitor up to a seven-mile radius. Their feeds are linked to a control center, where agents can track suspicious people and vehicles over a larger area. Smaller types of fixed towers provide additional camera surveillance.

A Border Patrol surveillance tower stands near the Rio Grande River bank in Hidalgo County, Tex. (Carolyn Van Houten/The Washington Post)

Planes and helicopters

PROS Carry some of the most sophisticated surveillance equipment in the CBP’s arsenal.

CONS Expensive; require a lot of maintenance and personnel.

Fixed-wing surveillance planes often have under-mounted infrared cameras and powerful night-vision equipment on board. If radar pings something, Air and Marine officers on board can verify what it is and follow along, alerting law enforcement on the ground.

“There are parts of the border where you don’t want to apprehend as soon as you see someone,” said Nuñez-Neto. “You want to be able to keep eyes on them but let them get to a part of the border where you have the tactical advantage.”

Planes are mostly used for reconnaissance, but helicopters often transport people and help with search and rescue.

A CBP helicopter flies over as a group of men who crossed the U.S. border illegally and tried to run from Border Patrol agents are detained in Mission, Tex., in August 2018. (Carolyn Van Houten/The Washington Post)

Satellite surveillance

PROS Another set of eyes.

CONS Expensive to use; can’t penetrate cloud cover; civil liberties concerns on U.S. soil.

Satellite images are used much like images collected by other air surveillance from remote places, Nuñez-Neto said. Agents will compare images taken of the same location at different times to look for changes, such as evidence of new or different patterns of foot traffic. Some people fear satellites will be able to zoom in on individuals.

Radio and cell data surveillance

PROS Can be used for search and rescue.

CONS Communication can be spotty in many areas.

The Department of Homeland Security says law enforcement may use commercially available location data “to identify the presence, but not the identity, of individuals within the border area." Isacson said narco-traffickers in Mexico and Colombia have been tracked by triangulating their cell signals.

In remote areas, cell coverage is new or nonexistent, so smugglers often communicate by radio or walkie-talkie, and Border Patrol can sometimes intercept their signals.

Mobile surveillance equipment

PROS Mobile; able to operate in extreme places.

CONS Older cameras have bad resolution; some types are not integrated with other systems; not automated, so people need to watch the feeds.

Agents need different types of on-the-go surveillance gear, such as portable radar, daytime and nighttime cameras and thermal imaging equipment that allows them to see for miles in the dark.

The largest and least-agile device in this category is an 80-foot tower on a trailer platform that can be driven (slowly) to new sites. It contains powerful Remote Video Surveillance System (RVSS) cameras, which send images to a central control center and were responsible for the discovery of at least one smuggling tunnel. (RVSS systems can be mounted on fixed towers, poles and buildings, as well.)

Other devices are truck-mounted, and still others are small enough to be handheld or perched on tripods. Many of the smaller devices don’t link to a control center.

A fixed surveillance tower stands in Mission, Tex. (Carolyn Van Houten/The Washington Post)

Specialized gear

PROS Allow agents to be faster and more effective.

CONS Agents in different areas need different equipment; off-the-shelf products rarely work in hot, sandy, windy environments.

Border agents and CBP officers have all kinds of additional devices to help them do their jobs. Among them are Defense Department surplus night-vision goggles, elemental isotype analyzers that can identify illegal substances, medical supplies and even gizmos that lasso the tires of fleeing vehicles. Some gear may be as simple as a stick that taps on cars so that well-trained ears can make sure that certain parts sound hollow, kind of like thumping a melon.


PROS Biometrics are a very effective way to cut through fraudulent documents and identify known criminals or people who may have previously used other identities.

CONS Readers and scanners can be glitchy and wear out quickly; facial recognition tech is new and is already raising privacy and civil liberties concerns.

Fingerprint readers often are used when agents in the field apprehend people and may also be used at ports of entry if officers have reason to believe a person is trying to enter the country illegally.

Biometric options beyond fingerprinting are becoming more robust and more precise, although they are not yet used at the U.S.-Mexico border. However, trials are underway at several airports and at least one seaport in which live photos and passport photos are matched so that your face is basically your boarding pass.

Patrol boats

PROS Can go places along the river that are hard to reach over land.

CONS Loud and easy to hear coming; some parts of the Rio Grande are too shallow to navigate.

While most agents and officers travel in SUVs, some ride ATVs, bikes, horses — and boats.

Air and Marine agents may carry cameras, radar and other equipment that helps them detect, track and intercept unfamiliar boats and look for smuggled goods. They also assist the Coast Guard and other law enforcement with disaster relief, searches and rescue operations.

Boats on the Mexican border are used mostly along the lower Rio Grande at the southern part of Texas. (The Coast Guard has jurisdiction on the coasts, so they’re the ones most likely to intercept drug boats headed to California, for instance.)

A CBP marine unit passes patrols the Rio Grande in August 2018 in Mission, Tex. Mexico is visible across the river. (Carolyn Van Houten/The Washington Post)

Dog teams

PROS Fantastic at finding whatever they’ve been trained to detect.

CONS Need lots of breaks, particularly in hot, desert areas; a tiny inhaled dose of ultra-potent drugs, such as fentanyl, can be deadly.

More than 1,500 CBP canine teams work on U.S. borders, and they are extremely successful at sniffing out drugs, weapons, currency and other contraband. They also help find people (and human remains), whether concealed in vehicles or lost in the wilderness.

On the Mexico border, dog teams operate primarily at ports of entry and checkpoints.

Dogs who successfully detect drugs — or people, such as in this simulation in Jamul, Calif. — are often rewarded with extra play time. (U.S. Customs and Border Protection)

Agents and officers

PROS Nothing happens without them.

CONS Very expensive (nearly all the CBP’s budget goes to salaries, said Nuñez-Neto); high turnover rate; months long hiring process.

Notice the word “agent” or “officer” appears in everyone of these descriptions? Without them, all the surveillance, barriers and devices are useless.

“If you don’t have the people available,” Isacson said, “you’re just watching movies of people doing bad things.”

However, hiring and keeping agents can be difficult. Nearly 17,000 Border Patrol agents worked at the southern border as of the end of 2017, down from an all-time high of 18,501 in 2013 according to CBP, despite more money earmarked for hiring.

That’s because the work is tough and dangerous, the pay is not great, Isacson said, and the jobs require living and working in desolate, undesirable areas. Hiring can take months because of rigorous security and background checks, and about 65 percent of applicants reportedly fail a mandatory polygraph test.

Nevertheless, those agents are the one piece of the border security puzzle that is absolutely necessary.

Border Patrol agent Robert Rodriguez reports a smuggler near the Rio Grande River in Hidalgo County, Tex., in August 2018. (Carolyn Van Houten/The Washington Post)

Joe Fox contributed to this report.

About this story

Additional sources: Spokesman Rick Pauza of the Laredo, Tex., office of U.S. Customs and Border Protection; CBP documents; General Accountability Office report on border security; Department of Homeland Security.

U.S. Customs and Border Protection photos from CBP Flickr page. Some illustrations are based on references from CBP photos.


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