Breath phone / mobile phone

We notice charging condition through screen. In fact ,when using mobileset, time taking the handset longer than watching the handset.
Breath phone shows charging condition as volume.
When charged completely, It is full, the battery get less, the volume get reduced.
So, we can make sure remain of battery without watching amount of battery through screen.
When turned off, as watching the volume , confirm the condition of charge or charge it.