sound the death knell of something

sound the death knell

To cause or signal the impending end or ruin of something, especially a business, organization, or activity. (Refers to the sound of a bell ringing—the knell—from a church to indicate that someone has died.) The expansion of the Internet and digital media has sounded the death knell for countless print-based businesses around the world.
See also: death, knell, sound

sound the ˈdeath knell of something

be the reason why something ends, goes out of fashion, or is replaced: The arrival of large supermarkets sounded the death knell of many small local shops.
The death knell is the ringing of a bell to announce a person’s death.
See also: death, knell, of, something, sound