Early versions of the inertial crash switches were too sensitive. I believe they've improved them to decrease false positives, based on an apparent reduction in reports. (Or, people have learned about them and how to reset them.)
In the early versions, any kind of aggressive driving -- hard braking, hard acceleration, hard cornering -- could trigger them. Rough roads -- washboards, pot holes, frost heaves -- caused the same problem. In some cases, a shopping cart bumping into your vehicle in a parking lot was enough.
I have heard a reliable report of someone swerving to avoid a collision. In that case, the car died during rush hour in the middle of an interstate highway. While the person's car wasn't hit, it did lead to multi-vehicle collisions and pileups.
I quit counting the number of people I've helped by resetting their switch. Almost all have tried to pay me. Three went as far as later leaving an envelope on my windshield, for a total of $80.
The inertial switch must be manually reset. If you think you have one ... or just want to make sure ... read your owner's manual or contact a dealership's customer service. In addition to knowing how to reset it, you need to know where it is. In sedans, they're typically located in the trunk, usually near the gas tank fill outlet. In vans and pick-ups, they're usually under the dash on the passenger's side. (I've had several people say, "Oh, that's what that is.")
Regardless of whether you have the switch or not, ALWAYS turn off the ignition (key) switch if you're involved in an accident. Provided you can do so safely. (If in doubt, get everyone well away from the vehicle to a safe place.). Turning off the ignition switch will prevent the electric fuel pump from spewing fuel out a broken fuel line.
Even if you have a mechanical fuel pump, turning off the ignition switch will de-energize major portions of the electrical system and reduce the possibility of an electrical fire due to sparks and short circuit from crash damage. (Turn off the headlights also but leave the emergency flashers on.)
