"Heidegger’s great breakthrough came when he first noted that usually we do not encounter entities as present in consciousness. This is already an artificial special case that occurs most often in the breakdown of entities. As long as [...} the hammer and screwdriver are working in your hands rather than shattering into tiny pieces, they tend not to be noticed. While phenomena in the mind are present or present-at-hand, entities themselves are ready-to-hand for Heidegger, remaining invisible as they work towards various purposes.
"Even this standard way of reading Heidegger turns out to be too superficial. He is not just giving us a difference between conscious perception and theory on the one hand and unconscious practical action on the other. Notice that even praxis reduces things to figures, since my use of a chair or hammer reduces it, oversimplifies it by interacting with only a small number of its vast range of qualities. The lesson from Heidegger is not that conscious awareness is the site of figure and unconscious praxis is the site of ground. Instead, the hidden ground is the thing itself, which is reduced, caricatured, or distorted by any relation we might have with it, whether theoretical or practical. And moreover, this is not just a special fact about human beings, but is typical even of inanimate relations." (Graham Harman 'Greenberg, Duchamp, and the Next Avant-Garde' Speculations V punctum books, Brooklyn NY 2014 pp.261f my emphases)
In this passage from a recent essay, Harman recapitulates salient features not only of his poor reading of Heidegger's Sein und Zeit but, above all, of his inadequate interpretation of the phenomena themselves.
i) He seems to think that, like his teacher Husserl, Heidegger is dealing with "consciousness" and what is "unconscious", which could not be further from Heidegger's shifting the site of the mind from a consciousness in a subject's interior vis-à-vis an external world of objects to the openness of the Da, exposed to which Dasein understands beings presenting themselves in this Da as such-and-such (the hermeneutic As).
ii) Re the famous broken hammer in Sein und Zeit that draws attention to itself: In use the functioning hammer remains unnoticed, or rather, to employ Heidegger's more precise term, "inconspicuous" (unauffällig), which by no means signifies that the hammer is "invisible", nor that its user is "unconscious" of it. Rather, in use, the hammer is understood in its usefulness without its user having to be specially focused on it. The user's attention is directed rather toward the task at hand of hammering, and his mind, his Da, understands what is necessary to do the task. The hammer in its usefulness is open to him, i.e. understood as a matter of course, and incorporated into his actions.
iii) From i) and ii) it can be seen that Heidegger is not at all "giving us a difference between conscious perception and theory on the one hand and unconscious practical action on the other".
iv) Postulating a "hidden ground [which] is the thing itself" amounts to a vain attempt at resurrecting the Kantian Ding an sich, which is beyond any insightful phenomenal access whatsoever. Only that which presents itself in the Da is open to Dasein at all. Accordingly, "inanimate relations" among things do not "distort" the "thing itself". It is only Dasein, from its perspective, that can understand "inanimate relations" at all, whether it be in daily life or theoretically. Such "inanimate relations" present themselves as such-and-such to Dasein's understanding in one way or another. It makes no sense to speak of "inanimate relations" in themselves, just as it is futile to speak of a Ding an sich, which is merely the untenable, self-negating imagining of something that is utterly beyond any possible human experience, i.e outside the Da. You're trying to imagine outside the Da from inside the Da, thus bringing what was supposedly outside, inside.
The Da itself is the three-dimensional ecstatic time-clearing as the sole (pre-spatial; it has no 'where') 'site' for occurrents of all kinds to present and absent themselves and so be understood by Dasein in one way or another by virtue of its being 'enpropriated' (vereignet) to the Da. Moreover, the quivering of the Da in any situation, period or even age is what enables Dasein's responsive attunement one way or another.
What Graham Harman offers is just one more way of failing to get over the metaphysical split between the conscious subject and the external object whose being supposedly is altogether independent from the subject. This relapse is presented, of course, as 'the next big thing'.
Further reading: Out of your mind? Parmenides' message.