Learn Russian: Датчики постоянно фиксируют каждое пробуждение. - The sensors constantly record every awakening.

It is a verbal noun meaning 'awakening'. It comes from the verb пробудить (to awaken/arouse). You can spot the root буд- which also appears in будить (to wake someone up) and будильник (alarm clock). The д changes to жд before the -ение suffix, which is a common consonant mutation in Russian.

Why is the borrowed verb фиксируют used here instead of a native word like записывают?

While записывать works well for recording audio, video, or writing things down, фиксировать is the standard technical term used for sensors, medical devices, or software registering a specific data point or an event.

What case is каждое пробуждение, and why does it look like the dictionary form?

It is in the Accusative case because it is the direct object of the verb фиксируют. Because пробуждение is a neuter inanimate noun, its Accusative form is identical to its Nominative form, and the modifier каждое behaves the exact same way.

How can I remember the word датчики (sensors)?