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The alarm clock of Aristotle
It was a hydraulic alarm clock which was invented by Aristotle so that he could wake up after a short time interval and thus dedicating more time to his studies. Although Diogenes Laertios who preserves the above testimony does not describe the technology of the mechanism, the technology of that time and the corresponding case of Plato's alarm clock allowed its reconstruction.
It consisted of a container with water which emptied with a selected (for each case) flow speed into another container which had a pivoted semicircular float. At the predetermined moment when the container filled, the float was reversed and the balls which were placed on its level surface fell into a bowl (or dish) causing a deafening noise.
SOURCES: "Diogenes Laertius, Lives and Opinions of Eminent Philosophers"