noun
sounding continuously; ringing nonstop
Describes a phone, alarm, buzzer, etc. that keeps sounding without stopping. Often implies annoyance or that it has been left unattended.
朝から電話が鳴りっぱなしだ。
The phone has been ringing nonstop since morning.
目覚まし時計が鳴りっぱなしで、うるさかった。
The alarm clock kept ringing and was annoying.
鳴る is the base verb 'to sound/ring'. 鳴りっぱなし is a noun meaning the state of sounding continuously.
Compound of the continuative form 鳴り (from 鳴る 'to sound') + っぱなし (suffix meaning 'leaving something in a state').