Yep, since the advent of variable valve timing many cars that are designed to operate on premium can pull back on their advanced timing in order to accommodate lower octane fuel, by using the knock sensors to detect premature detonation.

Mine does not.

And even for cars that do, it is still not recommended to use lower octane fuel for a number of reasons. One of those is that you’ll tend to see decreased efficiency (MPGs) using the lower octane fuel - that alone may negate the savings you get on each tank fill. Another is that it takes a bit of time for the engine to fully adjust - it doesn’t just detect a single knock and immediately go into low octane fuel mode - and the accumulation of multiple early detonations can be harmful to the motor if the driver has a heavy foot and does not temper their acceleration habits while in the adjustment period. It can even cause the engine computer to run a slightly leaner fuel mixture, which tends to elevate exhaust temperatures and has the potential to damage downstream components - such as expensive catalytic converters - if subjected to repeated operation above optimal temperature.

Is it going to kill your car if you have to fill up in a pinch and only regular is available? No, you’ll very likely be fine. But you’re still better off filling with the recommended fuel grade - both in the short run (efficiency) and in the long run (operation outside of intended conditions).