noun
megaphone; bullhorn; loudhailer
A handheld or mounted device for amplifying the voice, used in crowds, events, or emergencies.
警察官が拡声器で避難を呼びかけた。
The police officer called for evacuation using a megaphone.
デモ隊は拡声器を使ってスローガンを叫んだ。
The demonstrators shouted slogans using bullhorns.
Compound of 拡声 (voice amplification) + 器 (device). The kanji 拡 means 'expand', 声 means 'voice', and 器 means 'instrument'.