Jeg ser efter, om døren er låst, før jeg går i seng.

No. In this sentence, ser efter means checks or looks to see.

So Jeg ser efter, om døren er låst means something like:

• I check whether the door is locked
• I look to see if the door is locked

This is not the same as English look after = take care of.

A useful comparison:

• at se efter noget = to check / look for / look to see about something
• at passe på nogen/noget = to take care of someone/something

So here, ser efter is about checking the door, not caring for it.

Here, om means whether or if in an indirect yes/no question.

The clause om døren er låst means:

• whether the door is locked
• if the door is locked

It is used because the speaker is checking the answer to a yes/no question:

• Is the door locked?
• Yes or no?

In Danish, om commonly introduces this kind of clause after verbs like:

• se efter = check
• vide = know
• spørge = ask
• undersøge = investigate

For example:

• Jeg ved ikke, om han kommer. = I don’t know if/whether he is coming.
• Hun spørger, om du er hjemme. = She asks if you are home.

Because om døren er låst is a subordinate clause, and Danish subordinate clauses usually keep the normal subject-verb order.

So you get:

• døren = subject
• er = verb
• låst = complement

That gives:

• om døren er låst

Compare:

• Direct question: Er døren låst? = Is the door locked?
• Indirect question: Jeg ser efter, om døren er låst. = I check whether the door is locked.

This is very common in Danish:

• Han spørger, om du kommer.
• not Han spørger, om kommer du.

Låst is the past participle of låse = to lock, but in this sentence it functions like an adjective describing the state of the door.

So døren er låst means:

• the door is locked

This usually describes a state, not the action itself.

Compare:

• Døren er låst. = The door is locked.
• Han låser døren. = He locks the door.
• Døren bliver låst. = The door is being locked / gets locked.

So in your sentence, the speaker is checking the result or condition: whether the door is in the locked state.

The commas mark subordinate clauses, which is very common in Danish writing.

The sentence is:

• Jeg ser efter, om døren er låst, før jeg går i seng.

Here:

• om døren er låst is a subordinate clause
• før jeg går i seng is also a subordinate clause

So the commas help show the structure.

Danish comma rules can be a bit tricky because there are slightly different systems taught and used, but commas before subordinate clauses like these are very normal and helpful for learners to notice.

Før means before.

In this sentence:

• før jeg går i seng = before I go to bed

It introduces a time clause that tells you when the checking happens.

You can use før in similar ways:

• Jeg spiser, før jeg går. = I eat before I leave.
• Luk vinduet, før du går ud. = Close the window before you go out.

Literally, går i seng means goes into bed, but idiomatically it means goes to bed.

This is a fixed and very common Danish expression:

• at gå i seng = to go to bed

Examples:

• Jeg går i seng klokken elleve. = I go to bed at eleven.
• Børnene er gået i seng. = The children have gone to bed.

So even though gå normally means walk/go, the whole phrase should be learned as one expression.

Because the sentence describes a habit or a normal routine.

• Jeg ser efter ... før jeg går i seng
  = I check ... before I go to bed

English also often uses the present tense for habits, and Danish does the same.

So this sentence sounds like something the speaker usually does, not just one one-time action.

If you wanted to make it clearly about the past, you could say:

• Jeg så efter, om døren var låst, før jeg gik i seng.
  = I checked whether the door was locked before I went to bed.

Yes, in many contexts.

Possible alternatives include:

• tjekker = check
• kontrollerer = check/inspect
• undersøger = examine/investigate

For example:

• Jeg tjekker, om døren er låst.
• Jeg kontrollerer, om døren er låst.

But ser efter sounds natural and everyday. It often suggests having a look to make sure.

So:

• ser efter = everyday, natural, a bit softer
• tjekker = very common, slightly more direct
• kontrollerer = more formal

Yes.

In Danish, the definite article is often added to the end of the noun instead of being a separate word.

So:

• dør = a door
• døren = the door

This is one of the big differences from English.

Here are the parts:

• dør = door
• -en = the definite ending for a common-gender noun

So døren er låst literally contains the idea door-the is locked, which in English becomes the door is locked.

Usually no, not in standard careful Danish for this meaning.

Here you need om because the speaker is checking whether something is true.

• Jeg ser efter, om døren er låst. = I check whether the door is locked.

Hvis usually means if in the sense of a condition:

• Hvis døren er låst, ringer jeg på. = If the door is locked, I ring the bell.

So a helpful distinction is:

• om = whether / if (yes-no content)
• hvis = if (condition)

English uses if for both, but Danish often separates them more clearly.