Use a cord pass-through plate.

That’s the safest way — a specialized plastic or rubber plate that sits in the window gap and seals around the cord. It prevents pinching, keeps weather out, and eliminates the trip hazard.

Just closing the window on the cord is dangerous. The cord gets crushed, which can cause internal damage, overheating, or a fire. It also leaves a gap for bugs and drafts. And if the cord is loose, someone trips and yanks the whole setup.

A proper pass-through kit costs about $10–15. It comes with a notch or slot for the cord, plus foam to seal the rest of the gap. Installation takes two minutes. Some models even include a cord hook to keep the slack off the floor.

If you don’t want to buy one, you can cut a small notch in a piece of foam weatherstripping. That works in a pinch, but the plate is better.

This is not where you save six bucks.