كاشف الدخان صالح للعمل.

Because كاشف الدخان is an iḍāfa construction, often called a genitive/possessive phrase:

• كاشف = detector / detector device
• الدخان = the smoke

Together, كاشف الدخان literally means detector of the smoke, which in natural English is the smoke detector or a smoke detector, depending on context.

A key point: in Arabic, an iḍāfa phrase becomes definite if the second noun is definite. Since الدخان has الـ, the whole phrase is definite. So كاشف الدخان is understood as the smoke detector.

It is an iḍāfa phrase:

• كاشف is the first term of the iḍāfa (المضاف)
• الدخان is the second term (المضاف إليه)

In this structure:

1. The first noun does not take الـ
2. The second noun is usually in the genitive case
3. The whole phrase acts like one noun phrase

So:

• كاشف الدخان = the smoke detector
• literally: detector of the smoke

Because in an iḍāfa construction, the first noun normally does not take الـ.

So Arabic says:

• كاشف الدخان = the smoke detector

not:

• الكاشف الدخان ❌

The definiteness comes from the second noun, الدخان, and spreads to the whole phrase.

صالح here is the predicate of the sentence, describing the subject كاشف الدخان.

So the sentence is a nominal sentence:

• كاشف الدخان = subject
• صالح للعمل = predicate

Here صالح means fit, suitable, in good working order, or serviceable, depending on context.

So the full sentence means something like:

• The smoke detector is fit for use
• The smoke detector is in working order

In present-tense Arabic nominal sentences, the verb to be is usually omitted.

So Arabic says:

• كاشف الدخان صالح للعمل
• literally: the smoke detector fit for use

But in natural English, we add is:

• The smoke detector is fit for use

If you wanted a past or future meaning, Arabic would usually use a verb such as كان.

صالح means suitable, fit, valid, or good enough, depending on context.

With لـ + noun, it often means:

• fit for
• suitable for
• good for

So:

• صالح للعمل = fit for work/use
• more naturally here: in working order, fit for operation, or working properly

In this sentence, العمل does not literally have to mean employment. It often means functioning/operation/use in practical contexts.

The preposition لـ here gives the sense of for.

So:

• صالح = fit / suitable
• للعمل = for work / for operation / for use

Together:

• صالح للعمل = fit for use or ready to operate

Because لـ is attached to العمل, the spelling becomes:

• ل + العمل = للعمل

This is very common in Arabic writing.

Because it is made from:

• the preposition لِـ = for
• plus العمل = the work / operation

When they combine:

• لِ + العمل → للعمل

So one lam belongs to the preposition, and the other belongs to الـ.

In pronunciation, these merge smoothly, so you hear something like lil-ʿamali.

In fully vowelled formal Arabic, it would typically be:

كَاشِفُ الدُّخَانِ صَالِحٌ لِلْعَمَلِ

Breakdown:

• كَاشِفُ = nominative, because it is the subject of the sentence
• الدُّخَانِ = genitive, because it is the second part of the iḍāfa
• صَالِحٌ = nominative, because it is the predicate of a nominal sentence
• لِلْعَمَلِ = genitive after the preposition لِـ

In everyday writing, these short vowels are usually omitted.

د is a sun letter.

That means in الدخان, the l of الـ is not pronounced separately. Instead, the د is doubled.

So it is pronounced approximately:

• ad-dukhān

not:

• al-dukhān

This is why in fully vowelled Arabic you may see a shadda on the د:

• الدُّخان

Yes, but كاشف الدخان صالح للعمل is the most straightforward and neutral order.

This is a normal nominal sentence:

• subject first
• predicate second

You might sometimes see different word orders in other contexts for emphasis, but for a simple statement like this, the given order is the most natural.

It can be both, depending on context.

Here it is an adjective/predicate adjective meaning:

• fit
• suitable
• serviceable

But صالح can also be a noun/adjective meaning:

• righteous
• good
• virtuous

Arabic words often have a range of meanings, and context tells you which one is intended. In a sentence about a device, صالح للعمل clearly means fit for operation/use, not morally righteous.

Yes, but the meaning would shift slightly.

• كاشف الدخان يعمل = The smoke detector is working
• كاشف الدخان صالح للعمل = The smoke detector is fit for use / in working order

The first focuses on the device currently operating or functioning. The second focuses on its condition or suitability for operation.

So both are possible, but they are not exactly the same.