The static-cling decals come in a 4-pack and cost under $7. Placed on the outside of your windows, the decals—which come in various shapes—look like frosted or etched glass.

Entrepreneur: Greyson MacLean, 13, creator of BrickStix, static-cling decals and stickers for embellishing plastic building blocks such as Lego and Mega Bloks. "Aha" moment: MacLean, who has built ...