Roomster car alarm

Hi Folks, New owner here..........I bought s/h Roomster 2 months ago. 2 days later left the UK and have just returned. I spend a deal of time abroad and have always disconnected the battery of my various cars to save charge for return starting. No problems until now.

The driver's manual tells me that should the battery voltage goes down the car alarm will be activated. Since this time I planned to be away for only two months I left battery connected.

QUESTION:- How can I leave the car locked with the battery disconnected without this happening ?

I presume the alarm will sound should the car be left (with the battery connected) long enough for the voltage to drop substantially - How long is this likely to take?

Any helpful comment will be appreciated

Snowgoose