अलार्म छह बजे बजता है।

बजना means to ring, to sound, or to go off (for things like bells, alarms, phones, etc.).

So:

• अलार्म बजता है = The alarm rings / goes off
• अलार्म छह बजे बजता है = The alarm rings at six o’clock

This is a very common verb for sounds made by devices or instruments:

• फ़ोन बज रहा है। = The phone is ringing.
• घंटी बजती है। = The bell rings.

In this sentence, बजता है is the normal habitual present form, so it usually means something like rings, does ring, or goes off regularly.

Because अलार्म is treated as a masculine singular noun in Hindi.

In the habitual present, the verb agrees with the subject in gender and number:

• masculine singular → -ता
• feminine singular → -ती
• plural masculine → -ते

So:

• अलार्म बजता है। = The alarm rings.
• घंटी बजती है। = The bell rings.
  (because घंटी is feminine)

This is why you get बजता है with अलार्म.

छह बजे means at six o’clock.

• छह = six
• बजे = o’clock / struck / at the hour

In everyday Hindi, X बजे is the normal way to say a clock time:

• एक बजे = at one o’clock
• तीन बजे = at three o’clock
• छह बजे = at six o’clock

So छह बजे is functioning as a time expression: at six.

Because Hindi usually expresses clock times directly with बजे.

So English at six o’clock becomes simply:

• छह बजे

You do not normally need a separate word for at here.

Examples:

• मैं पाँच बजे उठता हूँ। = I wake up at five.
• क्लास दस बजे शुरू होती है। = Class starts at ten.

So in this sentence, छह बजे already includes the idea of at six o’clock.

In standard Hindi, the habitual present is normally made with:

• verb stem + ता/ती/ते + होना

So here:

• बजता = ringing / rings (habitual participle form)
• है = is

Together:

• बजता है = rings / does ring

Leaving out है would sound incomplete in normal standard Hindi.

Compare:

• वह पढ़ता है। = He studies.
• अलार्म बजता है। = The alarm rings.

So है is an important part of the present habitual construction.

It normally means The alarm rings at six or The alarm goes off at six as a regular/habitual fact.

That is because बजता है is the habitual present.

If you want to say The alarm is ringing right now, Hindi usually uses the progressive:

• अलार्म बज रहा है। = The alarm is ringing.

So:

• अलार्म छह बजे बजता है। = The alarm rings at six.
• अलार्म बज रहा है। = The alarm is ringing.

Because that is very natural in Hindi word order.

Hindi often puts time expressions before the verb:

• मैं सुबह आता हूँ। = I come in the morning.
• वह सात बजे सोता है। = He sleeps at seven.

In your sentence:

• अलार्म = subject
• छह बजे = time expression
• बजता है = verb

So the structure is:

subject + time + verb

That said, Hindi word order is flexible. You could also say:

• छह बजे अलार्म बजता है।

This also means The alarm rings at six, but the emphasis shifts slightly toward the time.

It is a borrowed word, originally from English alarm, but it is very commonly used in Hindi.

Hindi often uses borrowed words for modern objects:

• अलार्म = alarm
• फ़ोन = phone
• ट्रेन = train
• बस = bus

Even though the word comes from English, it still behaves like a Hindi noun in the sentence, including gender agreement. Here it is treated as masculine, which is why the verb is बजता है.

A simple learner-friendly pronunciation guide:

• छह ≈ chhah
• बजे ≈ buh-JAY

A few notes:

• छ is an aspirated ch sound.
• छह can be tricky because of the final ह sound. In natural speech, pronunciation may be slightly reduced depending on the speaker, but learners should aim for something like chhah.
• बजे has stress roughly on the second syllable for English speakers: buh-JAY.

If reading Devanagari is new for you:

• अलार्म = alaarm
• छह बजे = chhah baje
• बजता है = bajtaa hai

Not if you mean a regular habit.

• बजता है = rings / goes off (habitually, regularly)
• बजेगा = will ring (future, one specific future event or general future)

So:

• अलार्म छह बजे बजता है। = The alarm rings at six.
• अलार्म कल छह बजे बजेगा। = The alarm will ring at six tomorrow.

Use बजता है for routine or repeated action, and बजेगा for future.

You usually put नहीं before the main verb form:

• अलार्म छह बजे नहीं बजता है। = The alarm does not ring at six.

In everyday speech, people often shorten this to:

• अलार्म छह बजे नहीं बजता।

Both are understandable, and the shorter version is very common conversationally.

Yes. Depending on context, बजता है can be translated in several natural ways:

• The alarm rings at six.
• The alarm goes off at six.
• The alarm sounds at six.

All of these are good English translations of अलार्म छह बजे बजता है।

The most natural one in everyday English is often The alarm goes off at six.

Here बजना is intransitive.

That means the thing itself makes the sound:

• अलार्म बजता है। = The alarm rings.
• घंटी बजती है। = The bell rings.

There is also a related transitive verb:

• बजाना = to ring / to play / to sound something

For example:

• वह घंटी बजाता है। = He rings the bell.
• वह गिटार बजाता है। = He plays the guitar.

So the contrast is:

• बजना = to ring, to sound
• बजाना = to ring something, to play something

Because Hindi clock-time expressions use बजे, not घंटा.

• घंटा means hour
• बजे is the normal form used when stating a clock time

So:

• छह घंटे = six hours
• छह बजे = six o’clock / at six

These are different ideas:

• मैं छह घंटे सोता हूँ। = I sleep for six hours.
• मैं छह बजे सोता हूँ। = I sleep at six o’clock.

That is why छह बजे is correct here.