Compass is a geomantic tool, which can help people judge the orientation and geomantic situation. Hanging a compass at the door of a city can play a certain role in exorcism, because the compass can help people adjust the indoor feng shui pattern, thus reducing unfavorable factors.
However, it should be noted that the compass is not omnipotent, and we can't completely rely on it to solve the problem. If you encounter some unsolvable problems, you need to combine other methods to solve them. In addition, when using the compass, you need to be careful not to let outsiders see or use it to avoid revealing confidential information.
In a word, the compass can be hung at the city gate from door to door, but it can play its greatest role only by paying attention to the correct use and precautions.