Battery Status; Summary Of Button Functions - Mobistel MBF-100 Benutzerhandbuch

To activate the mute function in a microphone, press the volume
down button [-] briefly for 1 sec.; this will mute your voice to the other
party while on a phone call. When the mute function is activated, you
will hear a periodic beeping sound. To release the mute function,
press and hold the volume down button [-] briefly for 1 s again.

[Battery status]

By pressing [+] and [-] simultaneously and then releasing them
briefly, the battery status is indicated by the number of red flashes
with a beep. The number of flashes could range from 1 to 4
depending on whether the battery is sufficiently charged.

[Summary of button functions]

Function
Power on
Power off
Volume up
Volume down
Car kit
status
Power off
Power on
Talking
Talking
31
Action
Press for 2 sec.
Press for 5 sec.
Briefly press the volume up
button [+]
Briefly press the volume
down button [-]