Making a much louder Lost Model Locator

http://www.radioshack.com/product/index.jsp?productId 62405 http://www.skykingrcproducts.com/accessories/lostmodel/lost_rc_model_alarm.html
I need to know how to get or make a device that feeds power to the above 102 decibel Radio Shack siren, only when the transmitter is turned off. The Lost Model Locator on the next link already does this, but, this device has much less range because it is not nearly as loud.
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On Thu, 08 Oct 2009 09:14:27 -0500, Peter Olcott wrote:

lost_rc_model_alarm.html
Use the SkyKing products for the signal processing, cut off it's sounder and replace it with an appropriate detector/amplifier for the siren.
If you're lucky they use a piezo that just needs power, and all you'll have to do is switch a transistor with it. If you're not lucky, they'll give some AC signal to the piezo, and you'll have to rectify and amplify it.
--
www.wescottdesign.com

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Maybe if I could just understand the signals coming form the receiver, I could hook up a relay to the very loud radio shack siren. The siren must have 12 volts. I am a software engineer.
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The signal from the receiver to the servo is a pulse that ranges from about 1mS to 2mS and the servo gets somewhere around 40-50 pulses per second, IIRC. Perhaps a diode to resistor to charge a capacitor to a comparator circuit would trigger when no pulses are present.
RogerN
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http://www.dimensionengineering.com/PicoSwitch.htm Maybe this could work? Its output might have to be wired through a relay so that on and off are toggled, and hopefully lost signal is interpreted as off, thus turning the siren on.
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