A triggered sensor that drew the attention of three Border Patrol agents, including one who was fatally wounded by gunfire, was one of many hidden along the border separating Arizona from Mexico.
Nicholas Ivie was shot and killed early Tuesday morning in the line of duty as he and two other agents investigated what it was that caused the sensor to emit a signal that it was disturbed.
Border Patrol and Homeland Security said the sensors are sometimes found by smugglers who dig them up and destroy them, making the agents' jobs even harder.
Authorities said the sensors are running 24 hours a day, seven days a week.
Operators in control rooms stand by to call out agents any time the sensors are triggered.
The sensors are about the size of a small suitcase. They're typically buried in a hole, then covered up, leaving a small antenna exposed.
The sensor gets tripped by movement - sometimes it's cattle, sometimes it's smugglers.
They're tripped as often as there is activity, and because there aren't any pictures, it takes agents responding to the sensor alarms to figure out what exactly they're dealing with.
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