When you get it, it means that you have won, when you would have otherwise lost (your attack was successfull, even though you aren't strong enough to defeat you opponent).

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You can't. They only increase when you are attacked, and decrease if you attack, or when the next turn arrives.

Being attacked is part of the game anyway, (as is attacking), and if you could change your alert status, everyone else would be doing it too, so you'd still be as much as a target as before.

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