Learn Hardcore Russian: Перед сном я хочу отключить телефон. - Before sleep I want to turn off the phone.

The noun сон (sleep) in the instrumental singular is сном.
So:
- сон = sleep (nominative)
- сном = (before/with/by) sleep (instrumental)

With перед you always put the following noun in the instrumental:

перед домом – in front of the house
перед сном – before sleep / before going to sleep

Could I say до сна instead of перед сном? What’s the difference?

You can say both, but there is a nuance:

перед сном – literally “before sleep”, very idiomatic, commonly used for evening routines:
- Перед сном я читаю книгу. – Before bed I read a book.
до сна – literally “until sleep / up to sleep”, sounds a bit more formal or neutral and is less idiomatic for everyday routines, though it’s correct:
- До сна осталось два часа. – There are two hours left until sleep.

In your sentence, перед сном is the most natural choice for “before bed” as a daily habit.

Why is it я хочу отключить and not something like я хочу, чтобы отключить?

In Russian, verbs like хотеть (to want) are followed directly by an infinitive, without чтобы:

Я хочу отключить телефон. – I want to turn off the phone.
Я хочу спать. – I want to sleep.
Я хочу поесть. – I want to eat.

The construction хочу, чтобы… is used when what you want is expressed with a different subject and a finite verb, not an infinitive:

Я хочу, чтобы ты отключил телефон. – I want you to turn off the phone.

Here, since I am the one doing the action, Russian uses хочу + infinitive: я хочу отключить.

Why is the verb отключить (perfective) used, not отключать (imperfective)?

Because this is about a single, complete action you intend to do: turning the phone off once, before sleep.

отключить – perfective: to turn off (once, to completion).
отключать – imperfective: to be turning off / to turn off habitually or repeatedly.

Compare:

Перед сном я хочу отключить телефон. – Before bed, I want to turn off the phone (each night, one complete action).
Я часто отключаю телефон на ночь. – I often turn off my phone for the night (habitual action).

With хочу + a one-time future result, the perfective отключить is natural.

What’s the difference between отключить and выключить for a phone? Can I use выключить here?

Yes, you can say both here; both are natural:

выключить телефон – to switch the phone off (the general, most common verb for turning devices off).
отключить телефон – to disconnect / cut off the phone, often implying turning it off or disconnecting it from the network.

Nuance:

выключить is the default “turn off (a device)” verb.
отключить can suggest cutting off a connection (network, electricity, service):
- отключить интернет – turn off/disconnect the internet.
- отключить электричество – cut the power.

In everyday speech, Перед сном я хочу выключить телефон sounds slightly more neutral and typical, but отключить is also fine.

Why is телефон in this sentence and not something like мобильный телефон or смартфон?

In modern Russian, телефон by default usually means a mobile phone or smartphone, unless the context clearly indicates an old-style landline.

You could say:

мобильный телефон – mobile phone
смартфон – smartphone

But in everyday conversation, people normally just say телефон:

Где мой телефон? – Where is my phone?

So отключить телефон is understood as turning off your mobile/ smartphone.

Why don’t we say мой телефон (“my phone”) here?

Russian often omits possessive pronouns like мой, твой when it’s obvious who the owner is, especially with:

body parts: Я мою руки. – I wash my hands.
personal items: Я забыл телефон. – I forgot my phone.

In this context, it’s naturally assumed you mean your own phone, so:

Я хочу отключить телефон. – I want to turn off the phone. (understood as my phone)

You can say мой телефон for emphasis or clarity, but it isn’t necessary.

What case is телефон in, and why does it look the same as the dictionary form?

Телефон here is in the accusative singular, because it is the direct object of the verb отключить.

For inanimate masculine nouns, the accusative singular form is identical to the nominative singular:

Nominative: телефон – (subject)
Телефон лежит на столе. – The phone is on the table.
Accusative: телефон – (object)
Я отключил телефон. – I turned off the phone.

So it’s the same form, but grammatically it’s accusative.

Can I put перед сном at the end and say Я хочу отключить телефон перед сном? Is there a difference?

Yes, that word order is also correct and natural.

Перед сном я хочу отключить телефон.
- Slightly more focus on the time frame (“Before bed, I want to…”).
Я хочу отключить телефон перед сном.
- Slightly more focus on the action (“I want to turn off the phone before bed.”).

Both versions are fine in everyday speech; the difference is mainly in rhythm and emphasis, not in meaning.

Is перед сном literally “before sleep” or “before going to bed”? Does it include the idea of “going to bed”?

Literally, перед сном means “before sleep”, but in everyday usage it functions very much like English “before bed” / “before going to bed”.

Typical collocations:

Перед сном я чищу зубы. – I brush my teeth before bed.
Перед сном не пей кофе. – Don’t drink coffee before bed.

So although the verb “go” isn’t there, перед сном naturally implies the period right before you go to sleep.