Image showing the small size of the micro- accelerometer used to trip a car 'air-bag' safety device. The micro-accelerometer is seen as the small black dot in the middle of the hand. In a collision, the micro-accelerometer detects the sudden slowing down of the car. This triggers a circuit which rapidly inflates a plastic bag with air. The air-bag deploys between the driver and the steering wheel, preventing serious facial injury as the driver is thrown forward. The air- bag inflates fully in about 0.2 seconds. Micro- accelerometers are mechanical devices made by the same processes that are used in the manufacture of conventional silicon microcircuits.