This is the 10112th most frequent Russian word.
бдительным
Alert or vigilant.
The word 'бдительными' is used as an adjective in the plural nominative case, describing the state of being alert and cautious.
Оставайтесь бдительными на дороге, чтобы избежать аварий.
Stay vigilant on the road to avoid accidents.
Here 'бдительны' functions as an adjective describing the personnel's characteristic vigilant nature in masculine plural form.
Сотрудники службы безопасности всегда бдительны, чтобы предотвратить угрозы.
Security personnel are always vigilant to prevent threats.
In this sentence, 'бдительным' is used as a singular masculine adjective in instrumental case paired with the verb 'быть', implying the necessity of staying alert.