Threshold devices present information gathered from the home's surroundings to give new views on the domestic situation. We built two prototypes of different threshold devices and studied them in field trials with participant households. The Local Barometer displays online text and images related to the home's locality depending on the local wind conditions to give an impression of the sociocultural surroundings. The Plane Tracker tracks aircraft passing overhead and imagines their flights onscreen to resource an understanding of the home's global links. Our studies indicated that the experiences they provided were compelling, that participants could and did interpret the devices in various ways, that their form designs were appropriate for domestic environments, that using ready-made information contributed to the richness of the experiences, and that situating the information they provided with respect to the home and its locality was important for the ways people engaged with them.

Ambiguity is usually considered anathema in Human Computer Interaction. We argue, in contrast, that it is a resource for design that can be used to encourage close personal engagement with systems. We illustrate this with examples from contemporary arts and design practice, and distinguish three broad classes of ambiguity according to where uncertainty is located in the interpretative relationship linking person and artefact. Ambiguity of information finds its source in the artefact itself, ambiguity of context in the sociocultural discourses that are used to interpret it, and ambiguity of relationship in the interpretative and evaluative stance of the individual. For each of these categories, we describe tactics for emphasising ambiguity that may help designers and other practitioners understand and craft its use.