My windows get the Halloween treatment every October and I look forward to it all year. Decorated windows look great from inside and from the street. Most of these ideas take minutes and use things you probably already own. Here are my favorites.
1. Stick paper bat silhouettes on the glass
Black paper bats are the fastest window decor I know. I cut simple bat shapes from black construction paper and tape them to the inside of the glass. A few bats look cute, but a whole swarm flying across one big window looks amazing. I place them at different angles so they look like they are mid-flight. From outside at night with the lights on behind them, the effect is perfect.

2. Line the sill with mini pumpkins
Mini pumpkins belong on every windowsill in October. I line them up in a row or cluster them in odd-numbered groups. White pumpkins look classy against the glass, and orange ones pop against white trim. They last for weeks and need zero care. If your sill is deep enough, you can put a small pumpkin in front of each pane for a neat repeating look.

3. Hang a small garland across the top
A garland across the top of the window frames the whole display. I use a short faux leaf garland or a string of paper ghosts. I hang it with small removable hooks so the paint stays safe. The garland draws the eye up and makes the window feel dressed instead of plain. When I take it down in November, the hooks come off cleanly.
4. Wrap fairy lights around the frame
Orange or warm white fairy lights around the window frame make everything glow after dark. I run a battery strand along the inside edge of the frame and hide the battery box behind the curtain. The light shining through the glass looks so welcoming from the sidewalk. I turn them on at dusk and the whole house feels festive.

5. Set white pillar candles in the window
A row of white pillar candles on the sill looks classic and a little bit haunted in the best way. I use the battery kind with a flicker so I never worry about flames near curtains. Different heights look better than candles that all match. In the evening, they cast the prettiest shadows across the room. My neighbors always compliment this one.
6. Hang a witch hat from the curtain rod
This one makes me laugh every time I walk past. I hang a simple witch hat from the curtain rod with a bit of fishing line so it looks like it is floating. Adding a tiny broom next to it sells the joke. It is the kind of touch kids remember. Mine hangs in the front window where trick-or-treaters can see it.
7. Press leaf decals onto the panes
Reusable window decals are made for this. I press fall leaf decals or little ghost shapes onto the glass in a loose scatter pattern. They stick with just water and peel off without a mark in November. My kids love helping with this one. We do one window together every year and they arrange the decals however they want.
8. Build a moon-and-cat silhouette scene
For the big living room window, I cut a large yellow paper moon and a black cat silhouette and tape them to the glass. The cat sits on the moon like in the old storybook pictures. With the room lights on behind it, the whole scene glows from the street. It takes maybe twenty minutes with scissors and paper. This is the window people slow down to look at.
9. Layer sheer curtains behind the decor
Sheer white curtains behind the decorations soften everything and make the window glow. During the day they filter the light beautifully. At night they turn the window into a soft backdrop that makes the silhouettes pop. I leave my sheers up year round, so this costs me nothing. They also hide the tape and hooks from inside the room.
10. Light a jack-o-lantern in the window at night
On Halloween night itself, I put a carved pumpkin right in the front window instead of on the porch. The battery candle inside makes the face glow through the glass. It looks fantastic from the street and stays safe from wind and rain. After the trick-or-treaters leave, I blow out the light and the season feels complete.
Conclusion
Windows are the easiest place to make a big Halloween impact with small effort. Paper silhouettes, pumpkins, and a strand of lights go a long way. Pick one window to start and see how fun it is.