be on alert

After raising her concerns with the WTA, the tournament's security team were informed and told to be on alert.

"Be careful, the enemy is losing in every direction," he added, telling them that this meant they were more likely to be on alert for infiltrators and spies.

The reaction to his killing exposed a deep-seated anger against the trillion-dollar industry, and on Tuesday, Altoona police told its officers to be on alert after receiving multiple emails and calls, including death threats from the public.

The school asked everyone on campus to remain indoors and be on alert.

When an airline or a manufacturer figures in a headline-generating episode, the media and the public tend to be on alert for other problems involving the company, even those that have little to do with the company or that might not even be significant enough to attract much attention from safety agencies.