Is this 3 mats that measure 58" long or 3 mats that measure 58" together?
It worked well for us, we had 3 mats 58" long. Dogs stay off the couch. Now we put one across the entrance to the kitchen and the dogs stay out of the kitchen.
Does it have batteries?
You can turn it on and off, but I left mine on all the time for about a week. Now, I just leave the pad on the furniture but turned off.
Will they work under the cushions so the pet's can't see them?
It depends how heavy the cushions are, but most likely they will not set the alarm off because it will be an even weight.
Can this be folded under a recliner to keep pets from going under and being hurt?
I have folded the long pads in half for use on a smaller chair.
Is it ok for outside furniture?
I don't think it would work for long if it's outdoors and gets wet, it has a battery in it.