BT BIG BUTTON + User Manual page 12

The batteries power the Message Waiting Indicator lamp.
The normal flash rate when messages are waiting is every
2 seconds. When the batteries are running low and a message
is waiting, the flash rate slows to once every 6 seconds.
2 Plug your BIG Button + into the
telephone socket
If you do not have a modern style socket, call BT on
Freefone 0800 800 150 and ask for a BT engineer to come
and fit the correct socket.
This may be a chargeable service.
BIG Button +_Issue 2_Edition 1_1.10.03
Battery low indicator
11