Increasingly museums are developing information systems and guides to be accessed from small mobile devices. Some of these initiatives utilise proprietary hardware and software that can require substantial development resources. More recently museums have had the option to target personal mobile devices, (e.g. Apple iPhone or Google Android handsets) which potentially require a lower investment cost on the part of the institution. While the sophistication of these handheld devices means that a large volume of information can be stored and displayed, the challenge for museums is to provide usable access via the small screen area available. Taking examples from work done during the development of the British Museum multimedia guide, this paper discusses the processes and techniques available for usability testing in a 'live' museum environment and shows how the use of low-cost usability and user testing techniques can be quickly fed back into the development process, making a valuable contribution to the ultimate design and effectiveness of the user interface.