US wireless earpiece maker Jawbone on Thursday apologized for a flaw that causes its fitness focused UP wristbands to go down and offered users their money back even if they keep the gadgets. UP is a wristband engineered to synch with software for iPhones, iPads and iPod touch devices to steer users toward better habits when it comes to eating, sleeping and being active. It was released by the San Francisco-based Jawbone in November. A troubling number of UP wristbands have failed, however, possibly due to a problem with capacitors in the devices designed to carefully track body movements. "This is unacceptable and you have our deepest apologies," Jawbone founder and chief executive Hosain Rahman said in an open letter to UP users. "We've been working around the clock to identify the root causes." Jawbone has studied wristbands returned for troubleshooting and discovered a problem with capacitors that are supposed to hold electrical charges, according to Rahman. Jawbone has replaced defective UP bands free of charge and is offering to give buyers their money back even if they keep working wristbands. UP bands cost $100. "We are so committed to this product that we're offering you the option of using it for free," Rahman said. Jawbone has temporarily stopped making UP wristbands but planned to resume productions after fixing the trouble. UP wristbands look like simple pieces of jewelry but sense body motions and sleep patterns to discern how many steps a wearer takes or how deeply people are slumbering. Users can even track their meals by using Apple gadget cameras to snap pictures of what they eat. Free UP software lets wristbands feed the information to iPhones, iPads, or iPod touch devices. UP presents data in bar graphs and timelines that expose patterns and show how close people are to achieving goals they set for themselves. It also has a social networking component.