Any shop will have them. I know most FS stores keep at least a couple in stock most of the time.

Personally I don't like the sirens with their own back up battery. I would rather get a pair of small 12v 7ah batteries and use them to battery back the whole alarm.

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Paul Niwranski
1966 Cadillac Superior Crown Royale Limousine Hearse

If you're mirrors ain't shakin...you got taken...
RIP Member #8
Be careful what you wish for...