Alarmcentralen sender brandvæsenet.

Because Danish usually puts the definite article at the end of the noun instead of using a separate word before it.

So:

• alarmcentralen = the alarm center / the emergency dispatch center
• brandvæsenet = the fire department / the fire service

This is very common in Danish. English says the + noun, but Danish often says noun + definite ending.

Those endings show both definiteness and gender.

Danish nouns have two grammatical genders:

• common gender → definite singular usually ends in -en
• neuter → definite singular usually ends in -et

In this sentence:

• en alarmcentral → alarmcentralen
• et brandvæsen → brandvæsenet

So the different endings are not random. They depend on the noun’s gender.

Yes, it is closely related.

• infinitive: at sende = to send
• present tense: sender = sends / is sending
• past tense: sendte = sent
• past participle: sendt = sent

In this sentence, sender is the present tense.

A very literal translation is sends, but in real English this sentence is often translated as dispatches, because that sounds more natural for emergency services.

Because Danish makes compound nouns as one word much more often than English does.

So alarmcentral is a single compound noun:

• alarm
  • central

Then the definite ending is added to the whole compound:

• alarmcentral
• alarmcentralen

This is completely normal in Danish. English often uses two words where Danish uses one.

Yes, and that is exactly why singular is normal here.

Brandvæsenet refers to the institution/service as a whole, not to one firefighter. Danish often uses a singular noun for organizations and public services.

So:

• brandvæsenet = the fire department / the fire service
• not one fireman

If you wanted to talk about the actual people, you would use a different word, such as:

• brandfolkene = the firefighters
• brandmændene = the firemen

This is the normal word order for a simple Danish main clause:

subject + verb + object

So here:

• Alarmcentralen = subject
• sender = verb
• brandvæsenet = object

This looks a lot like English in this example.

But Danish also follows the V2 rule in main clauses, which means the finite verb normally comes in the second position. If another element comes first, the subject moves after the verb:

• Nu sender alarmcentralen brandvæsenet.
  Now the dispatch center sends/disptaches the fire department.

So the sentence is simple, but it still fits the normal Danish pattern.

Not in this exact sentence.

With a plain definite noun, Danish normally uses just the ending:

• alarmcentralen
• brandvæsenet

You usually do not say:

• den alarmcentralen
• det brandvæsenet

However, if there is an adjective, Danish often uses both a separate article and the definite ending:

• den lokale alarmcentral
• det kommunale brandvæsen

So in your sentence, the forms without den/det are the correct ones.

A few pronunciation points are especially useful here:

• sender: the -er ending is usually weak, like a light uh sound.
• brand: the d is not pronounced like a strong English d at the end.
• væ in brandvæsenet has a vowel that English does not have exactly; it is not the same as va or vee.
• the final -et in brandvæsenet is usually weak, not a hard English t

A rough learner-friendly approximation might be:

• sender ≈ SEN-uh
• brandvæsenet ≈ BRAN-veh-seh-neth

That is only approximate, but it points you in the right direction. The exact Danish sounds are softer than English spelling suggests.

Grammatically, Danish has indefinite forms:

• en alarmcentral
• et brandvæsen

But in this sentence, the definite forms are the natural choice because it refers to a specific, identifiable service:

• the dispatch center
• the fire department

Using the indefinite forms here would sound odd in most normal situations, because emergency services are usually understood as specific institutions, not just any random alarm center or any random fire service.