Εκκενώνουμε το κτίριο όταν ακούμε τη σειρήνα.

Εκκενώνουμε is the 1st person plural present active form of εκκενώνω, so it literally means we evacuate or we are evacuating.

In a sentence like this, Greek often uses the present tense for:

• a general rule
• a routine action
• an instruction stated generally

So here it is best understood as something like we evacuate the building when we hear the siren.

Greek usually does not need subject pronouns because the verb ending already shows who the subject is.

So:

• Εκκενώνουμε = we evacuate

You could add εμείς for emphasis, but it is normally unnecessary:

• Εμείς εκκενώνουμε το κτίριο... = We evacuate the building...

Το κτίριο means the building.

It uses:

• το = the neuter singular definite article
• κτίριο = a neuter singular noun meaning building

It appears in the accusative case here because it is the direct object of Εκκενώνουμε:

• we evacuate what?
• the building

For this noun, the nominative and accusative forms are the same:

• nominative: το κτίριο
• accusative: το κτίριο

Όταν means when, while αν means if.

Here the sentence gives a normal trigger for an action:

• when we hear the siren, we evacuate the building

So όταν is the right conjunction.

Compare:

• Εκκενώνουμε το κτίριο όταν ακούμε τη σειρήνα. = We evacuate the building when we hear the siren.
• Θα εκκενώσουμε το κτίριο αν ακούσουμε τη σειρήνα. = We will evacuate the building if we hear the siren.

Because this sentence describes a habitual/general situation.

όταν + present tense is commonly used for repeated or general actions:

• όταν ακούμε τη σειρήνα = when we hear the siren

If you were talking about a specific future event, Greek would often use a different structure, for example:

• όταν ακούσουμε τη σειρήνα = when we hear the siren in the future / once we hear it

So:

• όταν ακούμε = habitual, general
• όταν ακούσουμε = future, one-time event

Both are possible in Modern Greek.

The full accusative feminine singular article is την, but before a consonant it is very often shortened in writing and speech to τη.

So:

• τη σειρήνα
• την σειρήνα

Both mean the siren.

The shorter form is extremely common in everyday Greek.

Greek uses the definite article more often than English.

Here τη σειρήνα can refer to:

• the expected siren in that situation
• the alarm signal in general
• the siren everyone knows about in that context

So even if English might say a siren, Greek very naturally says the siren.

It can mean both, depending on context.

• η σειρήνα = siren/alarm
• η Σειρήνα or οι Σειρήνες can also refer to the mythological Sirens

In this sentence, because of hearing it during an evacuation context, it clearly means alarm siren.

Yes. Greek word order is more flexible than English because the verb endings and articles help show the grammar.

The given sentence:

• Εκκενώνουμε το κτίριο όταν ακούμε τη σειρήνα.

Other possible orders:

• Όταν ακούμε τη σειρήνα, εκκενώνουμε το κτίριο.
• Το κτίριο το εκκενώνουμε όταν ακούμε τη σειρήνα.
  This version adds emphasis to the building.

The original order is neutral and natural.

It is pronounced approximately ek-ke-NO-u-me.

A few useful points:

• the stress is on -νώ-
• the double κκ is pronounced as a stronger k sound
• ου sounds like oo in food

So the whole sentence is roughly:

ek-ke-NO-u-me to KTI-rio O-tan a-KOU-me ti si-RI-na

That is only an approximation, but it helps with the rhythm.

Yes, especially in official, safety, or emergency contexts.

εκκενώνω is the standard verb for:

• evacuating a building
• clearing an area
• ordering people to leave for safety

A more everyday verb like αδειάζω can mean empty, but εκκενώνω is much better for emergency procedures.

So in this sentence, εκκενώνουμε το κτίριο is exactly the kind of phrase you would expect in a safety instruction.