Focus Mk4 Alarm battery backup sounder

[Minstrel]

I have an 18 plate focus Mk4 and the alarm sounder is going off when I lock the car, stops when I open the car the absence of any lights flashing initially confused me.

Luckily I found a kind garage that plugged me in and read that the battery in the back up sounder was below the required voltage and so let's you know by going into alarm mode, nice if they (Ford) could have added this to the dashboard display with all the rest of the info, I have been told that the battery should last 10 years ?

Anyway just wondered if anybody had any knowledge if this can be rescued with an internal battery change otherwise a new device costs £118.