The majority of creepy metallic sound effects in horror movies are made by one instrument: The Waterphone (aka Ocean Harp).
The waterphone is a modern invention influenced by a Tibetan drum, developed by Richard Waters in the early sixties. This bizarre instrument has been used in film scores and sound effects in movies as diverse as Poltergeist or Aliens.
Johan Söderqvist, who scored the 2008 version of Let the Right One In, is just one of the countless composers who have found inspiration in the waterphone:
“One of the things I try to do with every new picture is to find a unique sound, a new universe, which will suit the story and give it a musical personality. For Let the Right One In, I discovered an instrument called the bass waterphone, which I recorded endless samples of and then tweaked and worked into the fabric of the score. It defined the musical voice of this particular film.”