With planning an alarm install I would like to install "hidden" sirens that are only activated if power is lost to the alarm system or any components that may be tampered with during a break-in.

Example: Power wire to "puny" siren underhood is cut - trigger a relay to run voltage to a different series of sirens.

 

So what exactly is the question?

 

Yes they do make this. If you use a DEI alarm and backup battery, your alarm will sound if the battery is cut.

 

For clarification I am asking about a whole backup siren system that is a lot louder than the little siren that comes with the car. if they cut that siren or any other major component of the alarm so it doesn't make noise than have backups that are so loud that it would be hard to even stand less than 20 feet away.

 

I know of no system that will do that, you can get a backup batt. that will power the alarm if power is cut, or you can get a backup batt. siren that can be wired to the alarm or not, it will go off if power is cut, you could hide the alarms siren, wire a backup batt. siren to the alarm, run the "loop" of a closed loop sensor, [DEI 502T] along with the wires for the backup batt. siren, mount it so it can be seen, it has to be accessible anyway, to turn off if you need to disconnect the batt. if the wires to the backup batt. are cut, [along with the "loop"] the alarm will go off and so will the backup batt. siren, but your alarm should be going off as soon as anything is opened on your car, [hood, trunk/hatch or the doors] 94