החיישן פותח את התא הסודי.

A common pronunciation is:

ha-khayshan poteaḥ et ha-ta ha-sodi

A few notes:

• החיישן = ha-khayshan
  The letter ח is a throaty sound, like the ch in German Bach or Scottish loch.
• פותח = poteaḥ
  The last sound is again ח.
• את = et
• התא = ha-ta
• הסודי = ha-sodi

So the stress pattern is roughly:

ha-khay-SHAN po-TE-aḥ et ha-TA ha-so-DI

Here פותח means opens or is opening.

It is the masculine singular present-tense form of the verb לפתוח (to open).

In Hebrew, the present tense often covers both:

• The sensor opens the secret compartment
• The sensor is opening the secret compartment

The exact English translation depends on context.

את is the direct object marker.

Hebrew uses את before a direct object that is definite, meaning something like the..., this..., that..., a name, or something otherwise specific.

Here, התא הסודי means the secret compartment, which is definite, so Hebrew says:

• פותח את התא הסודי

But if the object were indefinite, Hebrew would usually not use את:

• פותח תא סודי = opens a secret compartment

So את does not itself mean a separate English word; it is a grammar marker.

Because in Hebrew, when a noun phrase is definite, the adjective also becomes definite.

So:

• תא סודי = a secret compartment
• התא הסודי = the secret compartment

Notice that both words get ה־:

• התא = the compartment
• הסודי = the secret

This is very normal in Hebrew adjective phrases.

Because in Hebrew, adjectives usually come after the noun.

So Hebrew says:

• תא סודי = literally compartment secret

not:

• secret compartment

This is one of the big word-order differences from English.

More examples:

• ילד קטן = small boy
• בית גדול = big house
• התא הסודי = the secret compartment

The subject החיישן (the sensor) is grammatically masculine singular, and פותח is also masculine singular in the present tense.

Hebrew present-tense verbs agree with the subject in gender and number.

Here are the matching forms of to open in the present tense:

• פותח = masculine singular
• פותחת = feminine singular
• פותחים = masculine plural
• פותחות = feminine plural

So:

• החיישן פותח = the sensor opens
• המערכת פותחת = the system opens
  (because מערכת is feminine)

Yes. Since everyday Hebrew is usually written without vowel marks, some words can be ambiguous in writing.

The letters פותח can also represent a passive past form in another context, depending on vocalization. But in this sentence, the structure makes the intended meaning clear:

• subject: החיישן
• verb: פותח
• object: את התא הסודי

So here it is naturally understood as active present:

The sensor opens / is opening the secret compartment

No. תא can have several meanings depending on context, including:

• cell
• compartment
• chamber
• booth in some contexts

So התא הסודי could mean different things depending on the situation, such as:

• the secret compartment
• the secret chamber
• the secret cell

If the sentence is about a device or mechanism, secret compartment is often the most natural translation.

Yes, but החיישן פותח את התא הסודי is the most straightforward and neutral order.

This is basically:

• subject + verb + object

Hebrew can sometimes move things around for emphasis, but for learners, this sentence is the standard pattern to focus on first.

So this order is a good model:

• החיישן = subject
• פותח = verb
• את התא הסודי = object

Because in Hebrew present tense, there is usually no separate word for am / is / are before a verb.

English says:

• The sensor is opening...

Hebrew simply says:

• החיישן פותח...

That same form can also mean:

• The sensor opens...

So the Hebrew present tense is often broader than the English one.