I bought one this evening and used it earlier on a muscle that’s been cramping at night in my lower back. I can’t really feel any difference right now, but if I’m not awakened with a knot in my lower back, I should assume it’s working, correct?
http://www.icyhot.com/smartrelief-back-hip/
It’s basically a non-prescription TENS unit. I also found the adhesive quite interesting, because it stuck the unit tightly to my skin and yet left NO residue when I pulled it off. 
It might work for some causes of back pain. For spinal stenosis, however, I haven’t been able to detect any benefit.
FWIW, I used it yesterday evening, and did not wake up with back cramps at all. 
Because they are so painful, it was worth every penny just to have relief this one night.
I had some cyclobenzaprine, and discarded it when I found the prescription had been filled in 2008.
This zombie is having back pain, and my doctor did give me more cyclobenzaprine, but I don’t want to use it unless absolutely necessary, so I got out this TENS unit and decided to order more refill pads - only to find out that the product has apparently been discontinued! Guess I’ll use it as infrequently as possible, unless I can find more pads.