Learn Hardcore Norwegian: Hun låser opp døren når jeg ringer på. - She unlocks the door when I ring the doorbell.

With a full noun object, the most natural order is particle before the object: Hun låser opp døren.
With a pronoun object, the particle goes after the pronoun: Hun låser den opp. (Not: Hun låser opp den.)

Why is it døren and not døra? Are both correct?

Yes, both are correct in Bokmål. Dør can be masculine or feminine:

Masculine: en dør – døren
Feminine: ei dør – døra Pick one gender for a noun and be consistent within a text. Døra often feels more colloquial/regional; døren can feel a bit more formal/traditional.

What’s the difference between låse opp and åpne?

låse opp = unlock (remove the lock, not necessarily open the door)
åpne (or colloquially lukke opp) = open (move the door so it’s open) So Hun låser opp døren may or may not include opening it; Hun åpner døren means she actually opens it.

Do I need the på in ringer på? What’s the difference from ringer?

Yes. å ringe på means “to ring (the doorbell).” Without på, å ringe usually means “to call (by phone).”

Doorbell: Jeg ringer på (døra).
Phone: Jeg ringer henne.

Could I say Hun låser døren opp instead of Hun låser opp døren?

It’s possible, but with a full noun object most speakers prefer låser opp døren. With a pronoun, you should place the particle after the pronoun: låser den opp (not låser opp den).

Why is it når here and not da?

når is used for present/future time and for general/habitual situations: Hun låser opp døren når jeg ringer på.
da is for single, specific events in the past: Hun låste opp døren da jeg ringte på.

Why are both verbs in the present tense if the meaning can be future?

Norwegian often uses the present tense to talk about future time in time clauses. Hun låser opp døren når jeg ringer på can mean a general habit or a future event depending on context. You don’t need “will” in Norwegian here.

What’s the word order rule in the når clause?

In subordinate clauses (like those starting with når), the subject comes before the verb: når jeg ringer på (not: når ringer jeg på). That lack of verb-second is a key difference from main clauses.

If I put the når clause first, does the main clause change?

Yes, main clauses are verb-second. If you front the når clause, you invert subject and verb in the main clause:

Når jeg ringer på, låser hun opp døren. (verb-second: låser before hun)

Do I need a comma in the original sentence?

No comma is needed when the når clause comes after the main clause: Hun låser opp døren når jeg ringer på. If the når clause comes first, add a comma after it: Når jeg ringer på, låser hun opp døren.

Can I omit døren and just say Hun låser opp når jeg ringer på?

Yes. If it’s obvious from context (e.g., we’re talking about the front door), Hun låser opp når jeg ringer på is natural.

How do I negate this sentence correctly?

Place ikke after the finite verb in the main clause, and after the subject in the når clause:

Main clause negation: Hun låser ikke opp døren når jeg ringer på.
Subclause negation: Hun låser opp døren når jeg ikke ringer på. (less likely contextually, but grammatically shows placement)

Is ringe på døra more precise than ringe på?

Both are fine. ringe på already implies “the doorbell.” You can add an object for clarity or emphasis: ringe på døra / dørklokka / ringeklokka.

Any quick pronunciation tips for key words?

Hun: the u is rounded (like a high, fronted “oo”).
låser: å like the vowel in “law”; s is [s]; r is tapped or trilled.
opp: short o, double p is a strong consonant.
døren: ø like the vowel in British “nurse” but with rounded lips; final -en is a schwa-like vowel + n.
ringer: ng is like the “ng” in “sing,” then an r.