There’s no specific placement for these bags, as you can place them anywhere. They usually have an o-ring built into the bag to hang them around whenever you want to. You can hang them from curtain rods or hooks on the wall. Be mindful of the size of the room to see proper results. A small bag is usually enough for a room and more than enough for a car. However, for a bigger room, you may need multiple bags. Placing the bag higher would be a good practice as warm air usually moves upwards toward the ceiling. As a result, it’ll pass through the bags and purify. In a car, you can simply put it in the cupholder.