Heidegger makes the distinction between tools with are ‘ready-to-hand’ (zuhanden) and those which are ‘present-at-hand’ (vorhanden). We are, he says, only conscious of tools as tools when they are present-at-hand. When we are actively engaged in performing a task through use of the tool, we lose consciouness of the tool itself, which ‘withdraws’ into the task.
The ready-to-hand is not grasped theoretically at all… The peculiarity of what is proximally ready-to-hand is that, in its readiness-to-hand, it must, as it were, withdraw in order to be ready-to-hand quite authentically. That with which our everyday dealings proximally dwell is not the tools themselves. On the contrary, that with which we concern ourselves is primarily the work.
Martin Heidegger, Being and Time, quoted in Paul Dourish, Where The Action Is
But this assumes exclusive modalities: we are either performing a task or not. It seems to say little about a world in which we seek constant ambient awareness. We want the tool to withdraw into the task, certainly, but what is the task? The easy answer is that it is being-in-a-context: being-at-work, relaxing-at-home, escaping-on-holiday. Each of those roles would call for activation of a different set of tools, which then withdraw themselves into the actions appropriate to that role. But I don’t think thats how it is. Extended awareness is analagous to metatools such as language; the task is that of being-in-the-world. There isn’t an off button.
As Ben points out, it is strange that ubiquitous computing is mostly treated as an engineering problem. It is not impossible that, 8000 years ago, writing was conceived as the mostly technological issue of flint-sharpening.