Лавинный датчик и свисток лежат здесь.

Because the subject is made of two things joined by и: лавинный датчик + свисток.

In Russian, when two singular nouns are connected by и and together form the subject, the verb normally goes in the plural:

• датчик и свисток лежат
• literally: the detector and the whistle are lying

So лежат is the 3rd person plural form of лежать.

They are in the nominative case, because they are the subject of the sentence.

You can see this in the basic dictionary forms:

• лавинный = nominative masculine singular adjective
• датчик = nominative masculine singular noun
• свисток = nominative masculine singular noun

So the sentence structure is basically:

• [Subject] лавинный датчик и свисток
• [Verb] лежат
• [Adverb] здесь

Because лавинный has to agree with датчик.

Russian adjectives change to match the noun in:

• gender
• number
• case

Here, датчик is:

• masculine
• singular
• nominative

So the adjective must also be masculine singular nominative:

• лавинный датчик

If the noun changed, the adjective would change too.

Grammatically, лавинный modifies only датчик.

So the phrase means:

• [лавинный датчик] и [свисток]

not

• [лавинный датчик] и [лавинный свисток]

If the speaker wanted the adjective to apply clearly to both nouns, they would normally repeat it or phrase the sentence differently.

Лежать literally means to lie or to be lying.

Russian often uses position verbs where English might simply say is/are:

• Книга лежит на столе. = The book is lying on the table.
• Ключи лежат здесь. = The keys are here / are lying here.

In this sentence, лежат suggests the objects are physically resting there, probably as loose objects rather than installed or standing upright.

Russian has no present-tense form of to be in ordinary sentences, so a verb like лежать helps express both existence and position.

Yes. Russian word order is flexible, and changing it usually changes emphasis, not the basic meaning.

For example:

• Лавинный датчик и свисток лежат здесь.
  Neutral: The avalanche detector and the whistle are here.

• Здесь лежат лавинный датчик и свисток.
  Emphasis on here or on what is located here.

• Лежат здесь лавинный датчик и свисток.
  Less neutral, more context-dependent, possibly stylistic.

The version you were given is a very normal, straightforward order.

Because Russian has no articles.

So:

• датчик can mean a detector or the detector
• свисток can mean a whistle or the whistle

The exact meaning depends on context.

In English, articles are required, but in Russian, speakers rely on context, word order, and shared knowledge instead.

Здесь means here.

It is an adverb of place, and it does not change form for case, gender, or number.

Examples:

• Я здесь. = I am here.
• Книга здесь. = The book is here.
• Они здесь лежат. = They are lying here.

In your sentence, здесь tells you where the detector and whistle are.

Not always exactly.

Датчик literally means something like sensor, detector, or device that detects/registers something. In real avalanche-safety terminology, English may use more specific terms like:

• avalanche beacon
• avalanche transceiver

So depending on context, лавинный датчик may be a general or approximate expression rather than a perfect technical match for one specific English term.

For learning grammar, though, the important point is that лавинный датчик is a noun phrase with:

• adjective: лавинный
• noun: датчик

A rough pronunciation guide is:

• Лавинный → la-VEEN-nyy
• датчик → DAT-chik
• и → ee
• свисток → svee-STOK
• лежат → lee-ZHAT
• здесь → zdyes’

A natural stress pattern is:

лавИ́нный дА́тчик и свистО́к лежА́т здЕ́сь

A learner should especially notice:

• ж in лежат sounds like the s in measure
• зд at the start of здесь can feel difficult at first
• final consonants and unstressed vowels may sound a bit different in natural speech

No, that is a good literal translation.

But in natural English, depending on context, people might more often say:

• The avalanche detector and whistle are here.
• The avalanche detector and whistle are lying here.

The Russian sentence naturally includes the idea of physical placement because of лежат, so the more literal English version is often helpful for understanding the grammar.