on the qui vive

[Thomassew]

lively attentiveness

[AliceAstes]

in a state of heightened vigilance, especially prior to battle

[Monty]

On the qui vive is a phrase that originated from French, meaning to be alert or on the lookout, to be watchful, vigilant, or in a state of readiness or preparedness. It is often used in situations where close attention or caution is required.