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The LO BAT message means, obviously and without question, a Low Battery condition.
This can result from one of a few causes:
1. the rechargeable backup power battery in the alarm system box has gone flat with age at last, and cannot hold charge. If that is the cause, then replacing the battery is the thing to start with.
2. the power line to the alarm system box may have been cut, or have failed, or have become otherwise inadequate. That can cause a low battery condition too, though it is much less likely and much less common... and should be quite easy to detect, too.
Let me know if you need further instructions, and I will advise you further.
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