There are certain times when you can make the safe, if terrifying, assumption that someone or something is haunting your house. Inanimate objects begin to take on a life of their own. Lamps, television sets, radios, and computers turn on and off without the intervention of a living human or a remote control. Windows open and close without help. Hanging lamps move from side to side unassisted by a breeze.
Curtains move without help.
Drinking glasses placed in perfectly fine, solid, safe locations suddenly tip over. Doors open and close without help. You see something a little out of the ordinary. You might see a face reflected in a glass or mirror, and when you turn around, no one is there. You hear something a little out of the ordinary.