One of the most important duties performed by a Border Patrol Agent is known as “line-watch”.  This involves the detection and apprehension of undocumented aliens and their smugglers by maintaining surveillance from a covert position, pursuing leads, responding to electronic sensor alarms, utilizing infrared scopes during night operations, using low-light level television systems, sighting aircraft, and interpreting and following tracks, marks, and other physical evidence.  In addition, Border Patrol Agents perform traffic checks, traffic observation, city patrol transportation checks, and other administrative, intelligence, and anti-smuggling activities.