We installed fire alarms to defend our house against fire.

The police are on alert to prevent illegal intrusion.

The police arrested him for trespassing on private property.

After the earthquake, he increased his precautions.

We always need to be vigilant against fraud.

He crossed the border illegally.

His actions were clearly illegal.

He went to the police station and reported the theft.

He always acts with a sense of caution.

He always has a high sense of alertness.