The Great Tit is known as one of the most varied songsters in Swedish ornithology — up to 40–50 distinct calls have been documented per population.
Song: a two-note, metallic "tea-cher, tea-cher, tea-cher" — clear and far-carrying. It can be heard as early as January in mild winters, peaking in April–May.
Contact call: a hard "pink-pink-pink".
Alarm call: a piercing "tsee-tsee".
Mimicry: the Great Tit can imitate Blue Tit, Jay and other species.
Recordings can be found on xeno-canto and on the taxon page of Artportalen (the Swedish species observation system).