It was a hydraulic alarm clock which was invented by Plato. The upper ceramic vessel supplied the next vessel with water through a tap (appropriately calculated provision for each case). When the second vessel was full at the programmed moment (e.g. after 7 hours), it emptied quickly through an axial siphon to the next airtight vessel and forced the contained air to come out with pressure, whistling through a syringe at its top. Because the flute led to water, the vibrating sound length produced a chirp with notes of different frequency. After its operation, the third vessel emptied slowly (through a small hole located at its bottom) to the lower storage vessel in order to be reused.