Ezekiel 33:2-5

Ezekiel, son of man, warn your people by saying: Someday, I, the LORD, may send an enemy to invade a country. And suppose its people choose someone to stand watch and to sound a warning signal when the enemy is seen coming. If any of these people hear the signal and ignore it, they will be killed in battle. But it will be their own fault, because they could have escaped if they had paid attention.