Sofa Scram MatHigh Tech Pet Pad Dog and Cat Repellent

What causes the unit to continually give a high pitched buzzing sound?

My 50 lb dog lays on the ground and digs at the front of the couch. If I could hang it along the base of the couch would it work when he digs at it?

How long does noise last after sitting on sofa scram? I accidentally sat on it, had to turn the alarm off, because it would not shut off. Defective?

Will this work for 5 lb dog?