280–220 BC).[28] Alarm clock 3rd century BC The Hellenistic engineer and inventor Ctesibius (fl. 285–222 BC) fitted his clepsydras with a dial and pointer for indicating the time, and added elaborate "alarm systems, which could be made to drop pebbles on a gong, or blow trumpets (by forcing bell-jars down into water and taking the compressed air through a beating reed) at pre-set times" (Vitruv 11.11).[29] Odometer c. 3rd century BC Odometer, a device used in the late Hellenistic time and by Romans for indicating the distance travelled by a vehicle.