by Arthur Conan Doyle

At this moment he fell back upon his pillow as if he had been shot, while the same look of horror came over his face which I had observed when I first entered the room. At the same instant there came, apparently from the air immediately above his bed, a sharp, ringing, tinkling sound, which I can only compare with the noise made by a bicycle alarm, though it differed from this in having a distinctly throbbing character. I have never, before or since, heard any sound which could be confounded with it.