Disattiviamo la sirena a patto che tutto sia finito.

Disattiviamo comes from disattivare, meaning to deactivate, to disable, or to turn off.

Grammatically, it is the first-person plural present form, so it can mean:

• we deactivate / we turn off
• or, depending on context, let's deactivate / let's turn off

That second meaning happens because Italian often uses the noi form as a way to say let's ....

Because Italian usually drops subject pronouns when the verb already makes the subject clear.

In disattiviamo, the ending -iamo already tells you the subject is noi (we). So noi is unnecessary unless the speaker wants emphasis.

For example:

• Disattiviamo la sirena = We turn off the siren / Let's turn off the siren
• Noi disattiviamo la sirena = We turn off the siren, with extra emphasis on we

Here, la sirena means the siren or the alarm siren.

Yes, sirena can also mean mermaid in other contexts, but not here. The verb disattivare makes it clear that this is some kind of device or alarm, not a mythical creature.

Italian uses articles more often than English does. In this sentence, la sirena means the siren, referring to a specific one.

English sometimes omits an article in broader contexts, but Italian usually keeps it with singular count nouns like this.

A patto che is a fixed expression meaning:

• provided that
• on condition that
• as long as

It introduces a condition that must be satisfied.

So the structure is basically:

main action + a patto che + condition

In this sentence, the idea is: we will deactivate the siren only if everything is over.

Because a patto che is the complete expression.

You should learn it as one chunk:

• a patto che = provided that / on condition that

The che introduces the following clause:

• a patto che tutto sia finito

You normally cannot remove che here.

Because a patto che requires the subjunctive.

Sia is the present subjunctive of essere.

So:

• è = indicative
• sia = subjunctive

Italian uses the subjunctive after expressions like a patto che, because the speaker is talking about a condition, not stating a simple fact.

So:

• a patto che tutto sia finito = correct
• a patto che tutto è finito = not correct in standard Italian

Sia finito is the passato congiuntivo, often called the present perfect subjunctive.

It is formed with:

• subjunctive of essere → sia
• past participle → finito

So:

• sia finito = has finished / be finished / be over, depending on context

Here it suggests that the condition is that everything must already be finished / over before the siren is deactivated.

Because tutto here means everything, and it is treated as a singular masculine word.

That is why you get:

• tutto = singular
• sia = singular
• finito = masculine singular

So tutto sia finito means everything be finished / everything be over.

If the subject were plural, you would change the verb and participle:

• tutti siano finiti = everyone / all of them are finished or have ended, depending on context

In practice, it works as part of the verbal expression sia finito, but it also carries the sense of finished / over.

So tutto sia finito is naturally understood as:

• everything is over
• everything has ended
• everything is finished

It does not mean that someone finished everything. That would be a different structure, such as:

• abbia finito tutto = has finished everything

That contrast is useful:

• tutto sia finito = everything is over
• abbia finito tutto = he/she has finished everything

Yes. That is a very common point of ambiguity in Italian.

The noi form can mean either:

• a simple statement: we deactivate
• a suggestion/proposal: let's deactivate

Which one is intended depends on context and tone.

So this sentence could mean either:

• We deactivate the siren, provided that everything is over
• Let's deactivate the siren, provided that everything is over

Often, yes, but the nuance is a little different.

• disattivare = deactivate / disable, often more technical
• spegnere = turn off, often more physical or direct

So:

• disattiviamo la sirena can suggest disabling the alarm system or stopping its function
• spegniamo la sirena can suggest simply turning the siren off

Both can be natural, depending on the situation.

You could express a similar idea with se, but the nuance changes.

Compare:

• Disattiviamo la sirena se tutto è finito = We turn off the siren if everything is over
• Disattiviamo la sirena a patto che tutto sia finito = We turn off the siren provided that everything is over

A patto che sounds more formal and more strongly conditional. It emphasizes that this is a required condition, not just a casual if.

Also notice the grammar difference:

• se usually takes the indicative
• a patto che takes the subjunctive