Il vigile del fuoco disattiva il rilevatore di fumo.

Because di + il contracts to del in Italian.

So:

• di + il = del
• di + lo = dello
• di + la = della
• di + i = dei
• di + gli = degli
• di + le = delle

In il vigile del fuoco, del fuoco literally looks like of the fire, but together the whole expression means firefighter.

It can be both, depending on context.

In this sentence, il vigile del fuoco most naturally means the firefighter or a firefighter, depending on the situation. Italian often uses the definite article il where English might sometimes use a or just a role name.

Also, vigile del fuoco is the standard Italian term for firefighter. It is a fixed expression, not something you usually translate word by word in normal use.

Italian uses articles more regularly than English.

Here:

• il vigile del fuoco = the firefighter
• il rilevatore di fumo = the smoke detector

Both vigile and rilevatore are singular masculine nouns, so they take il.

English sometimes drops articles in places where Italian keeps them, but in a normal full sentence like this, Italian usually includes them.

Disattivare is the infinitive, meaning to deactivate.

In the sentence, the verb is conjugated for the subject il vigile del fuoco:

• disattivare = to deactivate
• io disattivo = I deactivate
• tu disattivi = you deactivate
• lui/lei disattiva = he/she deactivates

Since il vigile del fuoco is third person singular, the correct form is disattiva.

It is the present indicative.

So the sentence is in the ordinary present tense: the firefighter deactivates the smoke detector.

As in English, this can sometimes describe:

• something happening now
• a habitual action
• a general statement
• an action in a narrative present

Without more context, the basic reading is simply present tense.

Di fumo means of smoke, and it works like smoke in smoke detector.

Italian often uses noun + di + noun where English uses two nouns together:

• rilevatore di fumo = smoke detector
• bicchiere di vetro = glass cup / cup made of glass
• scarpe da tennis = tennis shoes

So rilevatore di fumo is the normal way to say smoke detector.

Because di fumo here describes the type or function of the detector, not a specific smoke.

So rilevatore di fumo means detector for smoke / smoke detector, not detector of the smoke in a specific situation.

If you said del fumo, that would suggest some smoke or the smoke, which changes the meaning.

Compare:

• rilevatore di fumo = smoke detector
• l’odore del fumo = the smell of the smoke

Yes, it is completely normal.

The sentence follows the standard Italian order:

subject + verb + object

• Il vigile del fuoco = subject
• disattiva = verb
• il rilevatore di fumo = object

Italian can change word order for emphasis, but this version is the most neutral and straightforward.

It is the standard and safest term.

You may also hear pompiere, which is understood and fairly common in some contexts, but vigile del fuoco is the more official and standard expression in modern Italian.

So for learners, vigile del fuoco is usually the best choice.

The plural would be:

I vigili del fuoco disattivano i rilevatori di fumo.

Changes:

• il → i
• vigile → vigili
• disattiva → disattivano
• il rilevatore → i rilevatori

Notice that del fuoco stays the same in this expression, because it is part of the fixed phrase vigili del fuoco.

In this sentence, the article tells you:

• il vigile
• il rilevatore

The article il is used with singular masculine nouns.

Also, rilevatore ends in -e, which can be masculine or feminine in Italian, so the article is especially helpful there. Vigile also ends in -e, and again the article shows the gender.

So when learning nouns, it is a good idea to memorize them together with their article:

• il vigile del fuoco
• il rilevatore di fumo