Remote Start with existing factory alarm

You can use an auxilarily output off the factory alarm, such as power trunk, to fire the starter, but you lose the trunk function.  Some remote starters, such as the Crimesopper RS-900 can be triggered by locking the doors three times quickly with the factory remote.  Draw back is the range is limited to that of the factory unit.   You can replace the factory remote with the after market, but you'll do more work.

Thanks for the input, but I have another question. Where would I hook it up? Will i have to hook up the rs trigger to power door lock wires?MEH66

"Car Performance and Mobile Electronic Enthusiats"

yup....you connect the input trigger of the RS (one with the factory feature) to the lock wire of the vehicle, when the doorlock wire of the vehicle gets three pulses in a row, the RS will activate.  If you need the color and location of the factory RS wire, tell us your year and vehicle. I could even get you the factory keyless wire colors.