abyss

admonitory

alarm

alert

alien

beacon

beep

boom

buoy

caution

danger

dangerous

decompression

deep

device

dire

drone

eerie

emergency

float

floating

frightening

ghostly

guide

harbour

haunting

hum

maritime

marker

ocean

ominous

scary

sci-fi

scifi

sea

shore

signal

sinister

sonar

sonobuoy

spooky

submarine

submerged

supernatural

system

threatening

tone

undersea

underwater

warning

haunt

sci fi

submerge

threaten