Sartre identifies consciousness as an activity, making it nothing, no thing. He uses the metaphor of a flashlight illuminating a darkened room. Consciousness is the beam of light.
Another metaphor: Just as life is not something separate and apart from the processes carried out by living organisms, consciousness is not something separate and apart from the activity of an organism perceiving its environment via interaction.
Viewing consciousness as activity accords with phi, the theoretical measure of consciousness as information processing.
More generally, but also more speculatively, it also accords with Alfred North Whitehead’s pan-psychism, which imputed proto-consciousness to all levels of organization in his process philosophy. Consciousness is the process of interaction among concretion.