Thank you for your replies on whether a sensor can wear out. I now have more questions! The vendor says he has never been able to get his A17 back to work via Bluetooth to an iPAQ. He is running LC 11 and he doubts that his back is BT-enabled. Unfortunately, he is overseas and he cannot advise whether the BT symbol is shown on his back in the place I have seen it on other backs--in the battery attachment cavity. I was informed by one user that" The Aptus line was built a couple of years before LC11 came out. All Aptus backs already had bluetooth on-board which probably was a remainder from the Leaf Valeo Wi (wireless) backs. Bluetooth was disabled fairly quickly via firmware for the Aptus because Leaf had too many problems getting it to work properly. "With LC11 they also distributed new firmware for the Aptus back that enabled Bluetooth again so it could be used with the Wiview application. With installing the software, the software also updates the backs firmware (which is something to keep in mind when hooking up to an older version of the software). With new firmware you also get new features many times. "All Aptus backs have Bluetooth on-board depending on what firmware you have installed it is enabled. In the menu structure of the Leaf you can turn Bluetooth on or off." So, is it possible for an A17 back to not be BT-capable? Also, is it possible for an A17 with LC11 and BT turned on not to be able to communicate with a correctly selected and set up iPAQ? In other words, is it true that all A17s running LC11 and with BT turned on will definitely be able to communicate with an appropriate iPAQ? Apart from using a non-qualifying iPAQ, what could cause an A17 to be unable to communicate to the iPAQ?