atarasii mezamasidokei wo katta node, asita ha nebousinai hazu desu.

目覚まし時計 means alarm clock.

It is a compound word:

• 目覚まし = waking up / something that wakes you up
• 時計 = clock

So together, it literally gives the idea of a clock for waking you up.

In Japanese, adjectives usually come before the noun they describe.

So:

• 新しい目覚まし時計 = a new alarm clock

This works like English new alarm clock, although Japanese is much more consistently modifier before noun.

を marks the direct object of the verb.

Here, the verb is 買った = bought, so the thing being bought is:

• 新しい目覚まし時計を買った
• bought a new alarm clock

So を shows that 目覚まし時計 is what the speaker bought.

Because the sentence contains two different time relationships:

• 新しい目覚まし時計を買った = the speaker already bought a new alarm clock
• 明日は寝坊しないはずです = the speaker expects tomorrow not to oversleep

So the purchase happened in the past, and that past event is the reason for the expectation about tomorrow.

ので means because or since.

In this sentence:

• 新しい目覚まし時計を買ったので = because I bought a new alarm clock

It connects a reason to a result.

A useful way to see the whole structure is:

• Reason: 新しい目覚まし時計を買ったので
• Result/expectation: 明日は寝坊しないはずです

Both ので and から can mean because, but the nuance is a little different.

• ので often sounds a bit softer, more explanatory, and more objective
• から can sound more direct or more speaker-centered

So here:

• 買ったので、明日は寝坊しないはずです sounds like a calm explanation
• 買ったから、明日は寝坊しないはずです is also possible, but feels a little more direct

For learners, a simple rule is:

• use ので for a softer because
• use から for a more straightforward because

明日 by itself means tomorrow, and time words can often appear without a particle.

But 明日は adds the topic marker は, which gives a nuance like:

• as for tomorrow
• tomorrow, at least
• when it comes to tomorrow

So:

• 明日は寝坊しないはずです = As for tomorrow, I probably won’t oversleep

The は helps set tomorrow up as the topic or time frame being discussed.

Because the speaker is saying they will not oversleep.

• 寝坊する = to oversleep
• 寝坊しない = not oversleep

So:

• 明日は寝坊しないはずです = I should not oversleep tomorrow

The negative form is used because the expected result is not oversleeping.

はずです means something like:

• should
• ought to
• is expected to
• I have good reason to think

It does not mean absolute certainty. It expresses a strong expectation based on some reason.

Here, the reason is:

• I bought a new alarm clock

So:

• 寝坊しないはずです means I should not oversleep / I probably won’t oversleep

It sounds like the speaker is making a reasonable conclusion, not a guaranteed promise.

Because 寝坊するはずです would mean I should / am expected to oversleep, which is the opposite of what the speaker wants to say.

The logic of the sentence is:

• I bought a new alarm clock
• therefore, tomorrow I should not oversleep

So the negative form しない is necessary.

はず attaches to the plain form of verbs.

Examples:

• 行くはずです = should go
• 行かないはずです = should not go
• 来たはずです = should have come
• 来なかったはずです = should not have come

So here:

• 寝坊しない is the plain negative form
• 寝坊しないはずです = should not oversleep

This is the normal grammar pattern.

Yes, the subject is omitted, which is very common in Japanese.

The sentence does not explicitly say I, but the natural interpretation is:

• I bought a new alarm clock, so I probably won’t oversleep tomorrow.

Japanese often leaves out subjects when they are obvious from context.

A full version could be:

• 私は新しい目覚まし時計を買ったので、明日は寝坊しないはずです。

But in natural Japanese, 私は is often unnecessary.

Not exactly.

Because of はずです, it sounds more like:

• I expect I won’t oversleep
• I should be fine tomorrow
• There’s good reason to think I won’t oversleep

If the speaker wanted to sound more definite, they might choose a different expression. With はずです, there is still a little uncertainty.

The sentence follows this pattern:

Reason + ので, topic/time + expectation

Broken down:

• 新しい目覚まし時計を買ったので
  because I bought a new alarm clock
• 明日は
  as for tomorrow
• 寝坊しないはずです
  I should not oversleep

So the full structure is:

• Because I bought a new alarm clock, I should not oversleep tomorrow.

The spaces are usually just for learners.

Normal Japanese is typically written without spaces:

• 新しい目覚まし時計を買ったので、明日は寝坊しないはずです。

Textbooks and beginner materials often add spaces to make it easier to see the parts of the sentence.