You say that you wish you could put it it in another spot. My guess is that his arms are not working any longer because of muscle, so you really need to try a different area. I would also eliminate the numbing cream. We put the Navigator on her arms but have only used abs for the Dex with great results. I was told that ??? are always the sensor. We are at 15 months on this system, so I was concerned that we may need a new one. We have seen ??? a few times with this sensor, but the numbers always come back within an hour or two.