Door Closes When It's Not Supposed To

If you have a command block with a comparator next to it with the command (ex. /testfor @a[r=3]. Out of the comparator you have a signal leading to a door, and a lever that separately leads to the command block. When you flip the lever within the radius the door opens, out of the radius the door still closes even though it shouldn't and the comparator doesn't get powered.