Q. Consider the following actions:

1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode

In how many of the above actions is the function of accelerometer required? (UPSC Prelims 2023)
Answer: All three
Notes: The correct answer is [C] All three. An accelerometer is a micro-electromechanical system (MEMS) sensor that measures non-gravitational acceleration and can detect changes in orientation, vibration, and shock.

• Car Crash Detection (Action 1 – Correct): Airbag systems use high-range accelerometers to detect the rapid deceleration (negative acceleration) that occurs during a collision. If the deceleration exceeds a specific threshold, the sensor triggers the chemical reaction that inflates the airbag in milliseconds.
• Laptop Free Fall (Action 2 – Correct): Many laptops are equipped with a "3D DriveGuard" or similar protection systems. An accelerometer detects the state of "zero-g" or weightlessness that occurs during a free fall. It signals the hard drive to park its reading heads instantly to prevent them from crashing into the spinning platters upon impact, thus preventing data loss.
• Smartphone Tilt (Action 3 – Correct): Accelerometers in smartphones measure the direction of the Earth's gravitational pull relative to the device. By sensing the change in the gravity vector, the OS determines if the phone is being held vertically or horizontally and rotates the UI (Portrait/Landscape) accordingly.

While gyroscopes are often used alongside accelerometers in smartphones to provide more precise rotational data (angular velocity), the basic detection of tilt and orientation relies primarily on the accelerometer's ability to sense gravity.