keikoku wo yomimasita.

It is read:

けいこく を よみました
Romanized: keikoku o yomimashita

A few notes:

• 警告 = けいこく
• を is the object particle and is pronounced o
• 読みました = よみました

Also, Japanese is normally written without spaces, so you would usually see:

警告を読みました。

を marks the direct object of the verb—the thing that is being acted on.

Here, the verb is 読みました (read), so 警告 is the thing being read.

So the structure is:

• 警告 = warning
• を = marks warning as the object
• 読みました = read

In other words, what did someone read?
→ the warning

読みました is the polite past affirmative form of the verb 読む (to read).

Breakdown:

• dictionary form: 読む
• polite non-past: 読みます
• polite past: 読みました

So 読みました means read in the sense of did read / have read, with polite speech.

Because 読む is a godan verb, and when you attach ます, the final u sound changes to the i sound.

So:

• 読む → stem becomes 読み
• 読み
  • ました
• = 読みました

This same pattern happens with many godan verbs:

• 書く → 書きます
• 話す → 話します
• 待つ → 待ちます

So 読む → 読みます → 読みました is a normal conjugation pattern.

Japanese often leaves out the subject when it is clear from context or not important.

So 警告を読みました could mean:

• I read the warning
• He/she read the warning
• We read the warning

The sentence itself does not tell you who did it. You figure that out from context.

This is very common in Japanese and is one of the biggest differences from English.

Yes. Japanese usually puts the verb at the end.

This sentence follows:

object + particle + verb

So:

• 警告 = object
• を = object marker
• 読みました = verb

In English, you would normally say:

[subject] + read + the warning

In Japanese, it is more like:

[subject] + warning + object marker + read

So the word order is different, but the particle を helps show what role the noun plays.

Yes, it is grammatical and understandable, but it sounds somewhat formal or written.

警告 often means warning in a strong or official sense, such as:

• a warning sign
• a warning message
• a formal warning

Depending on context, Japanese might also use other words, such as:

• 注意 = caution
• 注意書き = warning note / caution notice
• 警告文 = warning text/message

But 警告を読みました is still a correct sentence.

In this sentence, yes: it is the past polite form, so it means that the reading happened already.

However, like English read, the exact nuance can depend on context. It can mean:

• read
• have read

But grammatically, it is definitely past.

If you wanted the non-past polite form, it would be:

• 警告を読みます = (I) read / will read the warning

Japanese does not have articles like a, an, or the.

So 警告 by itself can mean:

• a warning
• the warning
• just warning

Which one sounds best in English depends on the context.

That means when translating from Japanese into English, you often have to choose the most natural article yourself.

In casual speech, you would usually say:

警告を読んだ。

That is the plain past form of 読む.

Compare:

• 警告を読みました。 = polite
• 警告を読んだ。 = casual/plain

So the original sentence is appropriate when speaking politely, writing politely, or talking to someone you do not know well.