I have a friend who is a policeman, when he is away on nights etc. his wife has a mop handle under her bed, but the last 18 inches is painted matt lack, so in the event of her having to swing it in anger, the intruder wouldn't see the black bit in the dark, and would move out of the way of the bit he could see.
I am a climber, so have many sharp pointy things under the bed, although I find a 'Tony Martin lives here' sign on the gate to work extremely well.