The correct answer is All three.

Here’s how an accelerometer is involved in each action:

1. Detection of Car Crash/Collision

• An accelerometer detects rapid deceleration or impact forces, which triggers the deployment of airbags almost instantaneously.
• Function of accelerometer: Required.

2. Detection of Free Fall of a Laptop

• Accelerometers sense sudden free-fall motion (near-zero acceleration in free fall) and can signal the hard drive to turn off immediately to prevent damage.
• Function of accelerometer: Required.

3. Detection of Tilt of a Smartphone

• Accelerometers measure the tilt or orientation of the device relative to gravity, allowing the display to rotate between portrait and landscape modes.
• Function of accelerometer: Required.

An accelerometer is required in all three actions, as it plays a crucial role in detecting motion, orientation, or force changes in each scenario. Thus, the correct answer is All three.