smart
Refers to devices or technologies that are intelligent, connected, and often act independently.
Ein smartes Zuhause kann Heizung und Licht automatisch steuern.
A smart home can automatically control heating and lights.

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Refers to devices or technologies that are intelligent, connected, and often act independently.
Ein smartes Zuhause kann Heizung und Licht automatisch steuern.
A smart home can automatically control heating and lights.

'Smart' is a word borrowed from English (an Anglicism). Its meanings in German are therefore strongly influenced by the English original, but they are not always identical.
Diese neue App ist wirklich eine smarte Erfindung.
This new app is really a smart invention.
The most common use of 'smart' today is in connection with technology. It describes devices that are connected and intelligent. It is often part of compound words.
Mit meiner Smartwatch kann ich Nachrichten empfangen.
I can receive messages with my smartwatch.
When a person or an idea is described as 'smart', it means intelligent, skillful, or clever. It often has a positive connotation of deftness and efficiency.
Er ist ein smarter Verkäufer, er kann jedem alles verkaufen.
He is a smart salesman; he can sell anything to anyone.
The meaning 'elegant' or 'smartly dressed' is outdated in present-day German. You can find it in older texts or films, but it is better not to actively use it in modern everyday language.
In dem alten Film trug der Held einen smarten Hut.
In the old film, the hero wore a smart hat.
stupid / unfortunate
'dumm' and 'smart' can be opposites when it comes to thinking or acting. 'dumm' describes a person, idea, or decision as not clever. In this context, 'smart' means clever, skillful, or intelligent. 'smart' often sounds somewhat more modern and can also mean a practical, good solution. Important: 'smart' can also describe technical devices, for example 'ein smartes Gerät' (a smart device). In that case, it is not a direct opposite of 'dumm'.

Ihre Lösung für das Problem war wirklich smart.
Her solution to the problem was really smart.
Es war dumm, ohne Karte in die Berge zu fahren.
It was stupid to drive into the mountains without a map.