Larmet skyddar huset såvida inte tjuven stänger av det.

Såvida inte means unless.

So the structure is:

• main clause: Larmet skyddar huset = The alarm protects the house
• exception clause: såvida inte tjuven stänger av det = unless the thief turns it off

A useful thing to know is that såvida inte is a fixed expression. It is a bit more formal or written-sounding than very everyday alternatives.

In Swedish, the definite article is usually attached to the noun as a suffix.

So:

• ett larm = an alarm → larmet = the alarm
• ett hus = a house → huset = the house
• en tjuv = a thief → tjuven = the thief

This is one of the first big differences from English. Instead of saying a separate word like the alarm, Swedish usually says larmet.

Because det refers back to larmet.

The noun larm is an ett-word:

• ett larm
• therefore the pronoun is det

Compare:

• ett larm → det
• en bil → den

So stänger av det means turns it off, where it = the alarm.

Because stänga av is a particle verb, similar to an English phrasal verb like turn off or switch off.

The basic verb is:

• stänga av = to turn off / switch off

In the sentence, it appears as:

• stänger av = turns off

This is very common in Swedish. A verb plus a small word like av, på, upp, or ut often forms a new meaning.

Examples:

• sätta på = turn on
• stänga av = turn off
• gå ut = go out

So tjuven stänger av det is literally the thief turns off it, but in natural English: the thief turns it off.

Because såvida inte introduces a subordinate clause, and subordinate clauses in Swedish do not use the normal main-clause inversion pattern.

So here the order is straightforward:

• tjuven = subject
• stänger = finite verb
• av det = rest of the verb phrase

That gives:

• såvida inte tjuven stänger av det

This is normal subordinate-clause word order.

A useful detail: in this sentence, inte belongs to the fixed conjunction såvida inte, so you should think of it as one unit meaning unless, rather than as an ordinary not placed inside the clause.

Yes, Swedish could express the same idea in other ways.

A common alternative is:

• Larmet skyddar huset om inte tjuven stänger av det.

That also means The alarm protects the house unless the thief turns it off.

The difference is mostly style:

• såvida inte = a bit more formal, sometimes more written
• om inte = often more neutral and everyday

So såvida inte is correct and natural, but slightly more formal in tone.

Because modern Swedish usually does not require a comma before a subordinate clause.

So this is completely normal:

• Larmet skyddar huset såvida inte tjuven stänger av det.

You may sometimes see commas used for clarity or style, but in ordinary modern Swedish prose, leaving the comma out is standard.

Grammatically, tjuven means the thief, so it is definite singular.

But in sentences like this, Swedish often uses the definite form for the person involved in the imagined situation. It does not have to mean that both speaker and listener know exactly which thief is being discussed in real life.

So here it is best understood as:

• the thief in this scenario

If you wanted a more indefinite meaning, you could say:

• en tjuv = a thief

But the original sentence with tjuven sounds natural as a statement about a typical situation.

Both skyddar and stänger are in the present tense.

• skyddar = protects
• stänger = turns off

Swedish often uses the present tense for general facts, rules, or typical situations, just like English does:

• Larmet skyddar huset... = The alarm protects the house...

So the sentence is not necessarily talking about something happening right now. It is expressing a general condition: the alarm protects the house, except in the case where the thief turns it off.