Electronic Alarms and Home Security Devices - Power second siren from backup battery?

I want to add an external siren to a system that already has an interior siren. The panel (DSC Power1616) is only rated for 700ma, so the second siren would go over this limit. Instead of adding a second power supply I was thinking of driving the second siren by using a 12vdc relay powered directly from the backup battery leads. The relay would be signaled from the bell output. I'd put an inline fuse to protect the battery against shorts. This should allow the second siren to draw its power from the battery without overloading the panel. Has anyone done something like this before? Anything I should be concerned about? I really want to avoid adding a second power supply/battery/transformer just for the second siren. Any thoughts would be appreciated.

You would still be tapping the same basic power supply via the battery charging circuit. In short, while it sounds like a quick fix, it doesn't really work out that way.

Under normal circumstances, the battery is already the power "smoothing" device for the system. If you are going significantly past the rated system output, you need a power supply card.

Something simple and cheap like the ELK-624 will do the trick (ELK-P624 Power Supply (http://www.elkproducts.com/products/elk-p624.htm)). At the power level you are working with, it can even share the system transformer.

MrRonFL is 100% correct. If you are gonna get a relay go all the way with the power supply.

I, too dislike the low powered sirens that are available for the Simon XT. I am installing this at present. I am putting the Elk P112K power supply enclosure with battery backup on the wall behind my Simon XT panel. In it I am placing a Elk 912 relay. I will wire the relay to the siren output on the panel and to the siren. So the siren will be powered by a seperate power source. The Elk P112 puts out 1 amp and will power the DS 406 siren easily. I don't need more than that.The only thing I am concerned about is if the power is out and the Simon sends an alarm to the relay under 5 volts it won't trigger the relay which in turn won't set off the siren. The minimum for the relay to trigger is 5 volts. The Simon is supposed to put off 5.1volts from battery backup, I think, I HOPE. But not too sure. And, I wonder if it will be okay when it comes to a fire alarm signal. And if anyone know, should I still use a resister at the siren?
GI Joe

I, too dislike the low powered sirens that are available for the Simon XT. I am installing this at present. I am putting the Elk P112K power supply enclosure with battery backup on the wall behind my Simon XT panel. In it I am placing a Elk 912 relay. I will wire the relay to the siren output on the panel and to the siren. So the siren will be powered by a seperate power source. The Elk P112 puts out 1 amp and will power the DS 406 siren easily. I don't need more than that.The only thing I am concerned about is if the power is out and the Simon sends an alarm to the relay under 5 volts it won't trigger the relay which in turn won't set off the siren. The minimum for the relay to trigger is 5 volts. The Simon is supposed to put off 5.1volts from battery backup, I think, I HOPE. But not too sure. And, I wonder if it will be okay when it comes to a fire alarm signal. And if anyone know, should I still use a resister at the siren?
GI Joe

By default, you don't need a resistor.

Got the whole system up and running. The GE Simon XT. Hard wired a exterior siren with a Elk P112K power supply and relay. The siren I used is a ATW DS406 wired to warble. The siren is 117dB at 12VDC 1.0 amp. The first few tests and siren worked great. Then couple of days later when I forgot to disarm the system and entered the house I got a weird buzzing noise instead of a loud warble. I checked everything out and tested and it warbled. Tested again and buzzed. Buzzing is a weird type not to be confused with the steady tone if wired with the yellow. Sounds like the warble stuck in a hum. Manufacturer acts surprised and has never heard of the issue. ANyone else had this problem? Sounds like a bad siren to me. I wired it correctly and even removed the siren and wired straight to the power supply in the house, with no long wire run. Same intermittent buzz then warble. I even hooked straight into the backup battery and same thing. Distributor to send a call tag and then a replacement. Is it worth it? Or should I look for a higher priced replacement. I really liked the sound of the DS 406, (http://www.atwbrand.com/sounds/Sirens/DS-406warble.wav). Hard to find sound files for the other brands.
Thanks, GI Joe