ringing current การใช้

Fixed phones of the late 20th century and later detect this ringing current voltage and trigger a warbling tone electronically.
To alert the operator, or another subscriber on the same line, the subscriber turned the crank to generate ringing current.
The Trimphone was the first in the GPO range to use a tone caller which warbled at around 2000 Hz modulated by ringing current.
The various levels provided various tones, and ringing current of various durations and cadences ( especially valuable for tip side or ring side.
LED indicator lights on the front typically show signal strength and voicemail ringing current for more than one phone and one externally powered device, such as a telephone answering device or the base station for a cordless phone.