Hacen la revisión de seguridad hoy.

Because hacen is third-person plural of hacer.

• hace = he/she/it does or you do (formal singular)
• hacen = they do or you all do (formal plural)

In this sentence, the subject is understood as they—often meaning some unspecified people, such as staff, inspectors, or the people in charge.

Not necessarily. In Spanish, third-person plural is often used when the speaker does not name the people directly.

So Hacen la revisión de seguridad hoy can mean something like:

• They’re doing the security check today
• They do the security inspection today

The important idea is that someone is doing it, even if the sentence does not say exactly who.

Spanish often omits subject pronouns because the verb ending already shows who the subject is.

Here, hacen already tells you it is they. So adding ellos is usually unnecessary unless you want emphasis or contrast.

• Hacen la revisión de seguridad hoy. = normal
• Ellos hacen la revisión de seguridad hoy. = more emphatic, like They are the ones doing it today

Spanish often uses the definite article more than English does.

Here, la revisión refers to a specific, known procedure: the security check/inspection. Even if English might say They’re doing a security check today, Spanish commonly uses la when the speaker and listener both understand which review or inspection is meant.

So la revisión de seguridad sounds natural as the security inspection/check.

De seguridad means of security or, more naturally in English, security-related.

So:

• revisión = review, check, inspection
• de seguridad = related to safety/security

Together, revisión de seguridad means something like:

• security check
• security inspection
• safety inspection

The exact English translation depends on context.

Because the phrase is naming the type of review.

• revisión de seguridad = a review/check for security/safety purposes
• revisión segura = a safe review/check

Those mean different things.

So de seguridad classifies the noun, while segura would describe the noun’s quality.

Yes, hacer often means to do or to make, but it is also used in many common expressions where English uses different verbs.

In Spanish, it is very common to use hacer + noun:

• hacer una pregunta = to ask a question
• hacer una llamada = to make a call
• hacer una revisión = to do/carry out an inspection or check

So in this sentence, hacen la revisión means they carry out the inspection/check.

Grammatically, it is in the present tense, but in context it can refer to something happening today, including later today.

So it may mean:

• They’re doing the security check today
• They do the security check today
• Sometimes even They’re going to do the security check today, depending on context

Spanish often uses the simple present for near-future events when the time is clear.

Yes, hoy can move.

All of these are possible:

• Hacen la revisión de seguridad hoy.
• Hoy hacen la revisión de seguridad.
• La revisión de seguridad la hacen hoy. (more emphasis on today)

Putting hoy at the end is very normal and neutral. Moving it changes the focus or emphasis, not the basic meaning.

Yes. That is another very natural way to say it.

• Hacen la revisión de seguridad hoy = They do the security check today
• Se hace la revisión de seguridad hoy = The security check is done today / They do the security check today in a more impersonal way

The version with se sounds more impersonal and often more formal or institutional. The version with hacen feels a little more like unnamed people are carrying out the action.

They are similar, but not always identical.

• revisión often suggests a check, review, or going over something
• inspección often sounds more formal and can suggest a more official inspection

In many contexts, either could work, but revisión de seguridad is a very common phrase for a security or safety check.

You usually know from context.

In Spanish, seguridad can cover both ideas:

• security = protection against danger, crime, unauthorized access, etc.
• safety = protection from accidents or harm

So revisión de seguridad could be:

• a security check at an airport or building
• a safety inspection for equipment or a workplace

Context tells you which English word fits best.

The structure is:

[verb] + [direct object] + [time expression]

So:

• Hacen = verb
• la revisión de seguridad = direct object
• hoy = time expression

A literal breakdown is:

• Hacen = They do
• la revisión = the review/check
• de seguridad = of security / safety
• hoy = today

That is why the sentence feels very compact in Spanish.