chuui o shinai to, saifu o otoshite shimaimasu.

Yes, 注意 can mean caution, care, attention, or warning depending on context.

In 注意をする, it means to pay attention / to be careful.

A useful thing to know is that many Japanese nouns can combine with する to make a verb:

• 勉強する = to study
• 運動する = to exercise
• 注意する or 注意をする = to be careful / to pay attention

So here, 注意をしない means not paying attention or not being careful.

Because 注意 is being treated as the object of する.

Japanese often forms verbs like this:

• noun + をする
• or more compactly, noun + する

So both of these are possible:

• 注意をする
• 注意する

They mean basically the same thing here. The version with を can sound a little more explicit or slightly more formal in some contexts.

しないと is a casual way of expressing a condition, meaning something like:

• if you do not...
• unless you...

So:

• 注意をしないと = if you are not careful / unless you pay attention

This comes from the conditional と.

Very roughly:

• しない = do not do
• しないと = if you do not do it, then...

In warning sentences, this pattern is extremely common:

• 急がないと。 = If I don’t hurry...
• 勉強しないと。 = I have to study / If I don’t study...

Depending on context, 〜ないと can sound like either a plain conditional or an implied warning/obligation.

Not exactly. と is one way to say if/when, but it has a particular flavor.

It often expresses:

• a natural consequence
• something that regularly happens
• something that follows automatically

So in this sentence:

• 注意をしないと、財布を落としてしまいます。

the feeling is:

• If you’re not careful, the natural result is that you’ll end up dropping your wallet.

It is less about a one-time hypothetical choice and more about a likely consequence.

Because 落とす and 落ちる are different verbs:

• 落とす = to drop something (transitive)
• 落ちる = to fall (intransitive)

Here the wallet is the thing being dropped, so it is marked with を:

• 財布を落とす = to drop a wallet

If you said:

• 財布が落ちる that would mean:
• the wallet falls

Both can be possible in some situations, but 財布を落とす is the normal way to say drop your wallet.

〜てしまう adds extra nuance.

So:

• 落とします = drop it
• 落としてしまいます = end up dropping it / accidentally drop it / regrettably drop it

The helper verb しまう often suggests one of these feelings:

• the action is completed fully
• it happened unintentionally
• it is unfortunate or regrettable

In this sentence, 落としてしまいます gives the sense that dropping the wallet would be an unwanted mistake.

So the nuance is stronger than plain 落とします.

Because しまう attaches to the て-form of the main verb.

Pattern:

• verb て-form
  • しまう

Examples:

• 食べてしまう = eat it all / end up eating it
• 忘れてしまう = forget it completely / accidentally forget
• 落としてしまう = accidentally drop it / end up dropping it

So:

• 落とす becomes 落として
• then add しまいます

Because Japanese often uses the polite non-past form for general statements, future consequences, and warnings.

Here, しまいます does not specifically mean is doing right now. It can mean:

• something that happens in general
• something that will happen
• something likely to happen if the condition is met

So this sentence has the feeling:

• If you’re not careful, you’ll end up dropping your wallet.

Using ます simply makes it polite.

A casual version would be:

• 注意しないと、財布を落としてしまう。
• or even 注意しないと、財布落としちゃう。

The subject is omitted, which is very common in Japanese.

Depending on context, it could mean:

• If you’re not careful, you’ll drop your wallet.
• If I’m not careful, I’ll drop my wallet.
• If one isn’t careful, one may drop one’s wallet.

Japanese often leaves out subjects when they are understood from the situation.

In a warning like this, English learners will often interpret it as you, but the actual Japanese sentence itself does not explicitly say that.

It is understandable, but in everyday conversation, people often say more natural alternatives such as:

• 注意しないと、財布を落としてしまいます。
• 気をつけないと、財布を落としてしまいます。

A few notes:

• 注意する is common, and dropping the を is very normal.
• 気をつける is often the most natural everyday phrase for be careful.

So your sentence is grammatical, but many native speakers might prefer 気をつけないと in casual daily speech.

Yes, this is a very important point.

In many situations, 〜ないと can imply:

• have to
• need to

For example:

• 勉強しないと。 = I have to study.
• もう行かないと。 = I have to go now.

But in your sentence, because there is a consequence after it, しないと is functioning as a true conditional:

• If you don’t pay attention, ...

So context tells you which meaning is intended.

Yes, that is completely okay because they belong to different verbs.

Here is the structure:

• 注意をしないと
  • 注意 is the object of する
• 財布を落としてしまいます
  • 財布 is the object of 落とす

So each を marks the object of a different action.

Japanese can absolutely have multiple を particles in one sentence when they are tied to different predicates.

The sentence gives a warning about an undesirable result.

Its feel is something like:

• If you’re not careful, you’ll end up dropping your wallet.

The key parts of that nuance are:

• 注意をしないと = a warning condition
• 財布を落とす = the bad result
• 〜てしまう = accidental/unfortunate flavor
• ます = polite style

So the sentence is not just a neutral statement of cause and effect. It carries a mild sense of caution and regret about what might happen.