...
The main difference between devices is the type of installation. AV-04FD is a panel with flush-mounting installation, and AV-04SD requires wall-mounting installation.
Call button backlight statuses
The call button blacklight can display the following situations:
permanently lights in standby mode;
blinks rapidly during a call;
blinks slowly during a conversation;
blinks rapidly twice when the lock is opened.
Appearance
...