Which of the following is a type of sensor used in Linewatch operations?

The correct answer is seismic point sensors. These sensors are specifically designed to detect vibrations and movements in the ground, making them an effective tool for monitoring specific areas along the border. In Linewatch operations, which focus on surveillance and detection of illegal crossings or other activities, seismic point sensors can help agents identify the presence of individuals or vehicles traversing the terrain.

Seismic sensors can effectively provide real-time data about activity in remote locations, allowing Border Patrol agents to respond more quickly to potential illegal crossings. They are particularly valuable in areas where visibility is low or where traditional surveillance methods may be less effective.

While thermal vision, watchdog sensors, and radar detection are also technologies used in border security operations, they serve different purposes or operate in different contexts. Thermal vision is primarily used for detecting heat signatures from people and vehicles, while radar detection can be helpful in monitoring larger objects. Watchdog sensors may refer to a type of monitoring technology that is not as commonly recognized in the context of Linewatch operations. Thus, the specific use of seismic point sensors aligns with the needs of surveillance in Linewatch, making it the most relevant answer to the question.