Weathers suggests filling a spray bottle with two-thirds isopropyl alcohol and one-third water. Spray your icy windows with the solution, then quickly scrape away any slush left over. The spray should work because the freezing temperature of the solution is lower than the freezing temperature of water (32 degrees Fahrenheit).
It's a method also championed by David A. Katz, M.Sc., a chemistry professor at Pima Community College in Arizona, who recommended this mix to Men's Health. Though, Katz warns that the solution may refreeze if it's below zero outside.
If you absolutely need a solution for your frost-covered car windows, this is an easy one to make with things you have sitting under the sink. However, it's not a magic bullet. It won't cut through the seven inches of snow that fell last night. It's also not that far from the canned deicer or windshield washer fluid you can buy at the hardware store. Though, windshield washer fluid won't hit your side windows and deicer can be a little pricey.