Both with and without 'at' are very common. Device sentence is correct.
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Yoong LiatLook at how you're sleeping; your feet are dangling off/from the bed
Look how you're sleeping; your feet are dangling off/from the bed.
Goog catch, Liat. I was concentrating on the intended question of the preposition and failed to notice the punctuation problem. I think many would prefer a colon over a semi-colon