If you want to find out if you have demons do this simple exercise of self-control.

People can get demons in and on them without them even knowing!

If you want to find out if you have demons or not awaken at anytime when people in your home are asleep, and go into a room where you know you will not be disturbed and where there is the least amount of external stimulation. Sit upright in that dark room, no lights, no sounds, and try to rest without sleeping and without thinking about anything in particular. Sitting, and being diligent about sitting upright, will make it so that you cannot fall back asleep. You don't have to sit in a special position, the point is that you are not too comfortable to sleep but comfortable enough to continue with the exercise.

If you find yourself thinking about anything other than your surroundings catch yourself and bring your awareness back to yourself and surroundings of non-stimulation. Keep taking your thoughts captive and bringing yourself back to your surroundings; notice what you can about your surroundings with your eyes closed; your breath, skin, sensations, sounds, lights in your eyes, your body position - anything to get your mind off of wandering thoughts and focused on your surroundings. Don't THINK about anything in particular or for too long, not even your surrounding, just keep thinking of different things trying to keep your awareness on the "here and now", what you can sense. Make small observations of different things so that you stay awake. Keep doing mental body scans. Most likely your mind will begin to wander in la la land. When it does bring your attention back to here and now and again re-scan yourself and surroundings continually.

Do it only for 30 minutes. Your body will want to sleep since the moment you get up but it's a mental exercise where you are exerting control over your body and mind to not sleep or wander or be stimulated, not even with wandering thoughts. It's a boring process but well worth it when you find out the truth.