roguintuuti de husinna roguin ni kiduku.

A natural breakdown is:

• ログイン通知 = login notification / login alert
• で = by, through, via
• 不審なログイン = suspicious login
• に = marks the thing noticed
• 気づく = to notice / become aware of

So the basic pattern is:

[means/source] で [thing noticed] に 気づく

Here, で marks the means or trigger.

So ログイン通知で means something like:

• through login notifications
• by means of login alerts
• from a login notification

It does not mean location here. It is saying the notification is how you come to notice the suspicious login.

Because the two ログイン words are doing different jobs:

• ログイン通知 = a login notification
• 不審なログイン = a suspicious login

This is very normal in Japanese. The first is part of a compound noun, and the second is the thing being noticed.

So it is not awkward repetition in the Japanese sense.

ログイン通知 is a compound noun, basically login notification or login alert.

Japanese often combines nouns directly like this:

• 登録情報 = registration information
• 出発時間 = departure time
• ログイン通知 = login notification

You could sometimes express similar ideas with の, but direct noun compounding is very common, especially in tech, UI, and app language.

Because 不審 is a na-adjective.

When a na-adjective comes before a noun, it takes な:

• 不審なログイン = suspicious login
• 静かな部屋 = quiet room
• 便利な機能 = convenient feature

It is not an i-adjective, so 不審い is incorrect.

And 不審の is also not the normal pattern here.

Because 気づく usually uses に for the thing you notice.

The pattern is:

X に 気づく = to notice X / become aware of X

Examples:

• 間違いに気づく = notice a mistake
• 変化に気づく = notice a change
• 不審なログインに気づく = notice a suspicious login

So に is the normal particle with 気づく.

Because 気づく normally does not take the thing noticed with を.

In standard Japanese, the natural pattern is:

• X に 気づく

not

• X を 気づく

If you want a verb that more naturally takes を, you might use something like:

• 不審なログインを見つける = find a suspicious login
• 不審なログインを発見する = discover a suspicious login

But with 気づく, に is the expected particle.

気づく is not just to see. It means to notice, to realize, or to become aware of something.

It often suggests:

• you did not notice it at first
• then something makes you aware of it
• there is a moment of realization

So here, the idea is that the login notification helps you become aware that a login seems suspicious.

Japanese often leaves out the subject when it is obvious or not important.

In a sentence like this, the omitted subject is probably something general like:

• you
• the user
• one

This is especially common in:

• app text
• instructions
• ads
• feature descriptions
• headings

So the sentence sounds like a short feature statement rather than a full conversational sentence.

The dictionary form is very common in headings, labels, slogans, and product descriptions because it sounds:

• short
• neutral
• direct

In app or website Japanese, 気づく can feel like a feature tagline:
Notice suspicious logins through login notifications.

If you made it a more explicit polite sentence, it might become something like:

• ログイン通知で不審なログインに気づけます。
  = You can notice suspicious logins with login notifications.

So the dictionary form here is probably stylistic.

No. Standard Japanese is usually written without spaces.

So this would normally appear as:

ログイン通知で不審なログインに気づく。

The spaces are probably just there to help learners see the parts more clearly.