Look for the reset button.

Yes, that little rectangular button on the cord head or power strip is exactly what you’re looking for. If it’s there, the cord has thermal overload protection (usually called a circuit breaker or resettable fuse). When the cord gets too hot or you draw too much current, it trips and cuts power. You press the button to reset.

If there’s no button, there’s no built-in protection. That’s fine for lights or phone chargers, but I wouldn’t run high-draw stuff like space heaters or air conditioners on a cord without it. Also, check the cord for a “thermal overload” or “auto-reset” label—some cheaper ones have a non-resettable internal fuse that you can’t see, but that’s rare.

If your cord doesn’t have one, don’t run space heaters on it.