Matthew 24:42-44 NASB

Therefore be on the alert, for you do not know which day your Lord is coming. But be sure of this, that if the head of the house had known at what time of the night the thief was coming, he would have been on the alert and would not have allowed his house to be broken into. For this reason, you also must be ready; for the Son of Man is coming at an hour when you do not think He will.

Matthew 25:13 NASB

Be on the alert then, because you do not know the day nor the hour.

Luke 12:35-39 NASB

Be prepared, and keep your lamps lit. You are also to be like people who are waiting for their master when he returns from the wedding feast, so that they may immediately open the door for him when he comes and knocks. Blessed are those slaves whom the master will find on the alert when he comes; truly I say to you, that he will prepare himself to serve, and have them recline at the table, and he will come up and serve them. Whether he comes in the second watch, or even in the third, and finds them so, blessed are those slaves. “But be sure of this, that if the head of the house had known at what hour the thief was coming, he would not have allowed his house to be broken into.

Acts 20:29-32 NASB

Be on guard for yourselves and for all the flock, among which the Holy Spirit has made you overseers, to shepherd the church of God which He purchased with His own blood. I know that after my departure savage wolves will come in among you, not sparing the flock; and from among your own selves, men will arise, speaking perverse things to draw away the disciples after them. Therefore, be on the alert, remembering that night and day for a period of three years I did not cease to admonish each one with tears. And now I entrust you to God and to the word of His grace, which is able to build you up and to give you the inheritance among all those who are sanctified.

1 Corinthians 16:13 NASB

Be on the alert, stand firm in the faith, act like men, be strong.

1 Peter 5:6-9 NASB

Therefore humble yourselves under the mighty hand of God, so that He may exalt you at the proper time, 7 having cast all your anxiety on Him, because He cares about you. Be of sober spirit, be on the alert. Your adversary, the devil, prowls around like a roaring lion, seeking someone to devour. So resist him, firm in your faith, knowing that the same experiences of suffering are being accomplished by your brothers and sisters who are in the world.