Le compteur communicant indique l’index de consommation.

Because compteur is a masculine noun in French, so it takes the masculine singular definite article le.

• le compteur = the meter / the counter
• If it were feminine, it would be la

This is something you simply have to learn with the noun.

Compteur communicant means a smart meter or communicating meter.

• compteur = meter, counter
• communicant = communicating, able to send information

In utility and energy contexts, compteur communicant is the standard term for a meter that can transmit data automatically.

In French, many adjectives come after the noun, unlike in English.

So:

• un compteur communicant = a communicating/smart meter

This is a normal French word order. English often puts the descriptive word before the noun, but French frequently puts it after.

Yes. Here, communicant functions as an adjective describing compteur.

It comes from the verb communiquer, but in this sentence it behaves like an adjective meaning able to communicate / transmitting data.

So compteur communicant is a fixed technical expression.

Because French uses elision before a vowel sound.

• le becomes l’ before a word beginning with a vowel or silent h
• index begins with a vowel sound, so le index becomes l’index

This is very common in French:

• l’homme
• l’école
• l’index

Not here. In this context, index means the meter reading or registered value shown by the meter.

So in utility or technical French, l’index de consommation refers to the consumption reading or usage index, not a book index.

This is a more technical meaning of index.

De consommation means of consumption or for consumption/usage.

It specifies what kind of index we are talking about:

• l’index = the index / reading
• l’index de consommation = the consumption reading

French often uses noun + de + noun where English may prefer a compound noun or a different structure.

Because the sentence is not saying that the meter shows consumption in a general sense. It is saying that it shows the consumption index/reading.

So:

• la consommation = consumption, usage
• l’index de consommation = the consumption reading

The second one is more precise and more technical.

Indique is the third-person singular present tense of the verb indiquer.

So:

• indiquer = to indicate, to show
• il/elle/on indique = it indicates / it shows

Here, the subject is Le compteur communicant, so indique means shows or indicates.

Because the subject is singular:

• Le compteur communicant = the smart meter

That is one thing, so the verb must also be singular:

• Le compteur communicant indique ...

If the subject were plural, the verb would change:

• Les compteurs communicants indiquent ...

It is grammatical French, but it sounds somewhat technical or administrative, especially because of compteur communicant and index de consommation.

You might see this kind of sentence:

• in utility bills
• on energy company websites
• in user manuals
• in technical instructions

A more everyday explanation might use simpler wording, but this sentence itself is perfectly natural in the right context.

A French speaker would naturally parse it like this:

• Le compteur communicant = the smart meter
• indique = shows
• l’index de consommation = the consumption reading

So the structure is:

subject + verb + object

This is the same basic order as in English, even though some of the vocabulary is more technical.