A Ana falou com o porteiro pelo interfone, sem que a vizinha percebesse nada.

In European Portuguese, it is very common to use the definite article before a person’s first name: a Ana, o João, a Maria.

This does not usually mean the Ana in English. It is just normal usage in Portugal, especially in speech and informal writing. So A Ana falou... simply means Ana spoke...

The most common pattern is falar com alguém = to speak with / to speak to someone.

So:

• falou com o porteiro = spoke to the doorman
• falou com a vizinha = spoke to the neighbor

You may sometimes see falar a alguém, but falar com is much more natural in everyday Portuguese for this meaning.

Falou is the preterite of falar.

Here it shows a completed past action:

• A Ana falou com o porteiro... = Ana spoke / talked to the doorman.

It presents the action as a single finished event, not as an ongoing background action.

Pelo is a contraction of por + o:

• por o → pelo

So:

• pelo interfone = through the intercom / via the intercom

Here por expresses the means or channel used to do something.

Compare:

• falou pelo telefone = spoke on the phone
• enviou por email = sent by email

Sem que means without ... followed by a full clause.

In this sentence:

• sem que a vizinha percebesse nada = without the neighbor noticing anything

Portuguese often uses sem que + subjunctive when the second part has its own subject.

Here the subjects are different:

• main clause subject: A Ana
• subordinate clause subject: a vizinha

That is why sem que fits very naturally.

Because it comes after sem que, which normally requires the subjunctive.

The idea is not presented as a simple fact, but as something that did not happen or was prevented:

• Ana spoke to the doorman
• and this happened without the neighbor noticing

So Portuguese uses the subjunctive in that subordinate clause.

Percebesse is the imperfect subjunctive, 3rd person singular, of perceber.

Here it matches the past-time setting created by falou:

• falou = past
• sem que ... percebesse = subordinate action viewed from that past moment

A present-time version would usually be:

• A Ana fala com o porteiro pelo interfone, sem que a vizinha perceba nada.

So:

• perceba = present subjunctive
• percebesse = imperfect subjunctive

In Portuguese, after negative or negative-like expressions such as sem, it is normal to use nada, ninguém, nunca, etc.

So:

• sem que a vizinha percebesse nada

is perfectly natural Portuguese, even though English usually says:

• without the neighbor noticing anything

Portuguese often uses nada where English prefers anything.

Not in the formal English sense of perceive.

In everyday Portuguese, perceber very often means:

• to notice
• to realize
• to become aware of

So in this sentence, percebesse nada is best understood as:

• noticed anything
• or realized anything

Yes, Portuguese can also use an infinitive structure, for example:

• A Ana falou com o porteiro pelo interfone, sem a vizinha perceber nada.

That is also grammatical. It is a bit more compact.

However, sem que + subjunctive is very common and very clear, especially when the clause has a different subject. For learners, it is a very useful pattern to recognize and use.

The part after the comma is an adverbial clause explaining how or under what circumstances Ana spoke to the doorman.

In Portuguese, it is very common to separate this kind of extra information with a comma:

• main statement: A Ana falou com o porteiro pelo interfone
• added circumstance: sem que a vizinha percebesse nada

The comma helps readability and makes the sentence structure clearer.