From Beyond

Dr. Edward Pretorius (Ted Sorel) is a scientist who has developed the Resonator, a machine which allows whoever is within range to see beyond normal perceptible reality. His assistant, Dr. Crawford Tillinghast (Jeffrey Combs), activates the machine and soon sees strange creatures in the air. When he is bitten by one of them, he urges Pretorius to turn the machine off. However, the crazed Pretorius refuses. Events transpire to the point where Crawford panics, fleeing outside. When the police arrive, they find Pretorius decapitated. Crawford is subsequently arrested and accused of murder.
Crawford is committed to a psychiatric ward, where he is treated by Dr. Katherine McMichaels (Barbara Crampton). After Crawford gives his account of Pretorius' death, Katherine orders that Crawford undergo a CAT scan, showing that Crawford's pineal gland is enlarged and growing. Convinced of Crawford's innocence, Katherine has him released to her custody, and plans on taking him back to Pretorius' house and the Resonator. They are accompanied by Detective Bubba Brownlee (Ken Foree), who investigated Pretorius' death.
Upon returning to the house, Katherine and Crawford rebuild the Resonator. Crawford reactivates the machine, which causes more creatures to appear. A severely deformed Pretorius, still alive, appears in the attic and tells the trio of a world beyond that is more pleasurable than normal reality. A panicking Crawford shuts off the Resonator, making Pretorius and the creatures vanish.
The next morning, Katherine insists that the Resonator could shed light on the victims of schizophrenia, as well as possible treatments and suggests that they turn the machine back on, but Bubba and Crawford disagree. While Bubba and Crawford are asleep, Katherine gets back up to feel the pleasure from the machine and turns it back on, bringing forth a worried Crawford and the now almost unrecognizable and mutated Pretorius. Bubba enters the scene as Pretorius grabs Katherine, preparing to eat her mind and take her to the world of beyond. Crawford and Bubba go down into the basement to shut off the power, but encounter a giant worm-monster. Bubba succeeds in shutting off the power, rescuing Crawford and Katherine and sending Pretorius away.
When Bubba decides that they should leave the house, all of a sudden, Pretorius somehow returns and the Resonator turns back on, as all three of them run up into the attic to deactivate it. Katherine and Crawford are attacked by little bee-like creatures, and as Bubba pushes them out of the way, he is devoured to the bone. Crawford fights off Pretorius and succeeds in freeing Katherine, but then his enlarged pineal gland pops out of his forehead. Katherine short circuits the machine by spraying it repeatedly with a fire extinguisher.
She then takes Crawford back to the hospital, where she is evaluated for insanity and schizophrenia, since her story was just like Crawford's. As Katherine is being prepared for shock treatment by a sadistic staff member, Crawford has developed an overwhelming hunger for human brains and kills Dr. Bloch (Carolyn Purdy-Gordon). Katherine escapes and drives back to the house with a bomb and a crazed Crawford following her.
Katherine puts the bomb on the Resonator and goes to leave when Crawford attacks her. As he is about to eat her brain, she bites off his pineal gland, reverting him to his senses. However, Crawford is pulled away and eaten by a completely deformed, mutated Pretorius. Katherine finally escapes, right as the whole attic explodes.
She lands on her legs, breaking one, and as the neighbors gather around her, she goes from sobbing to laughing hysterically as she tells them, "It ATE him!".

Question: Who turns off the power?
Answer: Bubba