Work in ubiquitous computing and ambient intelligence tends to focus on information access and task supportsystems informed by the office environment, which tend to view the whole world as an office, or on surveillancesystems that feature asymmetric information access, providing interpretations of activity to a central authority. Thealien presence provides an alternative model of ambient intelligence; an alien presence actively interprets abstractqualities of human activity (e.g. mood, social energy) and reports these interpretations, not to a central authority, butback to the user’s themselves in the form of ambient, possibly physical displays. The goal of an alien presence is nottask accomplishment and efficient access to information, but rather to open unusual viewpoints onto everydayhuman activity, create pleasure, and provide opportunities for contemplation and wonder. The design of an alienpresence is an interdisciplinary endeavor drawing on artificial intelligence techniques, art practices of creation andcritique, and HCI methods of design and evaluation. In this paper we present preliminary work on the TableauxMachine, an alien presence designed for the home environment, as well as discuss a number of general design issuesof alien presence including co-interpretation, authorship, richness of expression vs. system complexity, tensionsbetween viewing computation as a medium vs. as a model, issues of privacy, and evaluation.