Because of the growing spread of mobile and small devices (like PDAs, mobile phones, etc.), designers and developers of interactive systems have to consider user mobility and the dynamic context of use. In this paper we discuss the design criteria we have defined for developing handheld location-aware systems for indoor environments. We analyse some of the technologies currently available for this purpose and examine how to use them in order to obtain location-dependent information. We report on our experience in designing a location-aware guide for museum visitors and identify possible design criteria for this type of system, which uses automatic detection of a change in environment to trigger the presentation of multi-modal, context-dependent information through a hand-held guide.