"A lot of people innocent people and their pets have wound up dead during no knock raids in recent years in this country. A no knock raid is when officers can serve a warrant on a house without notifying the residents first. At all. Period. Without ringing the doorbell, calling first, a knock, nothing. Police typically do it in the middle of the night or in the wee hours of the morning, too, when people are more likely to be asleep. The majority of these raids arenít even for violent crimes or imminent threats to life and limb, but drug crimes."
This Is Why They Should Knock First: Multiple Cops Shot, One Killed in No Knock Raid | The Daily Sheeple

No-Knock Warrant | Wex Legal Dictionary / Encyclopedia | LII / Legal Information Institute