The Devil is a threat. If he were not, the Bible would not warn us so often about his power and his ways. But the good news is that neither the devil nor his demons can influence us against our will. The way we can stand against the devil is by pleading the precious blood of Jesus Christ. That is our main source of strength whenever Satan tries to attack us.
Some preachers see a demon under every rock.
Every time one has a sniffle they suggest that the affected individual is under the control of a demon. That's bad theology. Jesus said there are some sicknesses that are for the glory of God. Take Lazarus, for example. When it occurs, it will usually be through disease and sickness.