1. Be on the alert for anyone acting suspiciously.

2. Knowing that danger threatened, they were on the alert.

3. Drivers must be on the alert for traffic signals.

4. Police are warning the public to be on the alert for suspicious packages.

5. They want to be on the alert for similar buying opportunities.

6. Police warned the public to be on the alert for suspected terrorists.

7. The patrol police on duty are on the alert against any possible disturbances.

8. You should always be on the alert for anyone who looks suspicious.

9. They were to stay on the alert for any soldier unlucky enough to go overboard.

10. Above, our full combat air patrol was on the alert.

11. Hearing this, I was instantly on the alert.

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12. She always on the alert for some new calamities.

13. The sentries were all on the alert.

14. An early warning system puts everyone on the alert.

15. Troops are on the alert against any possible aggression.

16. The Armies were constantly on the alert not to be taken by surprise.

17. These are the Chinese need to be on the alert.

18. They were constantly on the alert not to be taken by surprise.

19. Police are warning the public be on the alert for suspicious packages.

20. Her fears had always been on the alert for an upheaval.

21. The policemen were on the alert for an excaped convict.

22. They should also be on the alert for the attack of typhoon.

23. She was always on the alert for some new calamities.

24. The manager clicks on the alert, and the portal displays his current task list which now includes the task to approve the employee's travel.

25. Knowing that danger threatened , the sentry was on the alert.

26. They must be constantly on the alert for the enemy.

27. The city must be on the alert for being polluted.

28. Employees of oil companies in the city have been warned to be on the alert for anyone acting suspiciously near their offices.

29. They did their best to keep on their guard [ on the alert ] .

1. Drivers must be on the alert for traffic signals.