Mr 4 was a placid kid and a deep voice saying no made him stop what he was doing 95% of the time at 12 mths old.
Now Miss E, that's another story. Saying 'No' makes not one iota of difference. I say no, remove her hand. She still keeps attempting to touch the object that she is not allowed to touch. I end up removing her from the object, usually sitting her across the otherside of the room which she is not at all happy about.
Should she be understanding "No, don't touch" by now. She is 12 mths old.