hi
i have one of these that is indicating that the mains is on and you have an internal battery failure.
turn off the mains and if the light goes out the battery is flat and you can undo the panel and get a new one.
If your not an electrician like me make sure you turn off the power before playing with it.
If the light stays on the battery is ok.
If you want to take the front off enter the engineer code which is usually 1234 and press prog.
the only problem you may have is if the previous owner has changed the engineer code from the factory set one most peole dont alter it.
Ed
April 2009