You will want to use /playsound minecraft:event.raid.horn hostile @a ~ ~ ~ 1. The 1 at the end is the volume, so if you can't hear it, turn it up. Personally, I could hear it at volume 100, and pretty well at 1000.

For more information on the command, here is the /playsound wiki.
For more information on sounds, here are all of the Java Edition sounds.

Edit:

For bedrock users, the /playsound wiki applies too, but as described in the site, the syntax is a little different. I don't have BE, so I can't test it, but I think the command should be /playsound raid.horn @a ~ ~ ~ 1 1 1. The first 1 is the volume, the next is the pitch, and the last is the minimum volume.

The full list of bedrock sounds can be found here. Make sure to click [show] on the page to expand the list.

You will want to use /playsound minecraft:event.raid.horn hostile @a ~ ~ ~ 1. The 1 at the end is the volume, so if you can't hear it, turn it up. Personally, I could hear it at volume 100, and pretty well at 1000.

For more information on the command, here is the /playsound wiki.
For more information on sounds, here are all of the Java Edition sounds.

Edit:

For bedrock users, the /playsound wiki applies too, but as described in the site, the syntax is a little different. I don't have BE, so I can't test it, but I think the command should be /playsound raid.horn @a ~ ~ ~ 1 1 1. The first 1 is the volume, the next is the pitch, and the last is the minimum volume.

The full list of bedrock sounds can be found here. Make sure to click [show] on the page to expand the list.

You will want to use /playsound minecraft:event.raid.horn hostile @a ~ ~ ~ 1. The 1 at the end is the volume, so if you can't hear it, turn it up. Personally, I could hear it at volume 100, and pretty well at 1000.

For more information on the command, here is the /playsound wiki.
For more information on sounds, here are all of the Java Edition sounds.

You will want to use /playsound minecraft:event.raid.horn hostile @a ~ ~ ~ 1. The 1 at the end is the volume, so if you can't hear it, turn it up. Personally, I could hear it at volume 100, and pretty well at 1000.

For more information on the command, here is the /playsound wiki.
For more information on sounds, here are all of the Java Edition sounds.

Edit:

For bedrock users, the /playsound wiki applies too, but as described in the site, the syntax is a little different. I don't have BE, so I can't test it, but I think the command should be /playsound raid.horn @a ~ ~ ~ 1 1 1. The first 1 is the volume, the next is the pitch, and the last is the minimum volume.

The full list of bedrock sounds can be found here. Make sure to click [show] on the page to expand the list.