The border patrol is strictly monitoring to prevent illegal immigration.

The police arrested the illegal alien.

We installed fire alarms to defend our house against fire.

This project is proceeding under rigorous supervision.

This area requires strict caution because earthquakes occur frequently.

He couldn't enter Japan due to visa issues.

He was denied entry into the country due to visa issues.

We are under 24-hour surveillance.

We observed the phenomenon all night long.

His actions were clearly illegal.