El control de acceso revisa el código QR.

Because both control and código are masculine singular nouns, and each noun phrase has its own definite article.

• el control de acceso = the access control / the checkpoint / the entry control
• el código QR = the QR code

In Spanish, articles are used more regularly than in English, so it is normal to see el twice in one sentence.

Control de acceso is a noun phrase that literally means something like access control or entry control.

Depending on context, it could refer to:

• a security checkpoint
• the person or staff controlling entry
• a system or device that manages access

So in real life, the sentence could describe either a human checking the code or a machine/system doing it.

Spanish often uses noun + de + noun where English might use another noun as an adjective.

So:

• control de acceso = literally control of access
• natural English: access control

This structure is very common in Spanish:

• tarjeta de crédito = credit card
• puerta de entrada = entrance door
• centro de salud = health center

Because revisa is the conjugated form, while revisar is the infinitive.

Here, the subject is el control de acceso, which is third-person singular, so the verb must also be third-person singular:

• revisar = to check / to inspect / to review
• revisa = he checks / she checks / it checks

So the sentence is grammatically complete because the verb is conjugated.

It is in the present tense.

Specifically, it is the third-person singular present indicative of revisar.

That form can mean several things in English depending on context:

• checks
• is checking
• does check

So this sentence could describe a general function or a current action.

Not exactly by itself, but it can fit that idea depending on context.

The core meaning of revisar is:

• to check
• to inspect
• to look over
• to verify

If a machine reads a QR code, Spanish might also use:

• escanea = scans
• lee = reads
• verifica = verifies

But revisa el código QR is still natural if the idea is that the code is being checked or validated.

This is the standard Spanish order:

subject + verb + object

• El control de acceso = subject
• revisa = verb
• el código QR = direct object

That is the most neutral and common word order in Spanish, especially in simple statements.

Spanish often uses the definite article when talking about a specific thing already understood in context.

So el código QR sounds natural if both speaker and listener know which QR code is meant, such as the one a person presents at the entrance.

If you remove the article and say revisa código QR, it sounds incomplete or unnatural in standard Spanish.

Because in Spanish, labels like this usually come after the noun they describe.

So:

• código QR
• código postal
• número de teléfono

English often puts the modifier first, but Spanish commonly places it after the main noun.

In Latin American Spanish, people usually say the letter names in Spanish:

• Q = cu
• R = erre

So código QR is typically pronounced something like código cu-erre.

In everyday speech, pronunciation can vary a little by country and speaker, but that is the standard idea.

It is singular.

The head noun is control, which is singular, so the article and verb are also singular:

• el control
• revisa

If it were plural, you would say:

• Los controles de acceso revisan el código QR

Not in Spanish grammar here. The sentence is clearly active:

• subject: El control de acceso
• verb: revisa
• object: el código QR

So the access control is doing the action.

A passive version in Spanish would look different, for example:

• El código QR es revisado por el control de acceso

But that sounds more formal and less natural in everyday use.

Yes, depending on what you want to emphasize.

Some common alternatives are:

• escanea el código QR = scans the QR code
• lee el código QR = reads the QR code
• verifica el código QR = verifies the QR code

Each one gives a slightly different nuance:

• revisa = checks
• escanea = scans
• lee = reads
• verifica = verifies

So revisa is a broad, flexible choice.