alarms using the factory keyless

Well if I'm not mistaken and I believe that I am not most alarms come with the standard option of being wired to unlock all the doors in the car when the alarm is deactivated and a relay can be used to used the remote start for the car, all these are standard options for any alarm.

Learn to evolve, EVOLUTION

hey what year is your mustang?

There are alarm packeges available which do not come with remote control handsets. They learn the frequency of the cars current handset as long as it does not have code hopping. It has the complete features of any other alarm less the annoyance of carrying two handsets.

I know this because I sell them here in Ireland. 

Never heard of an alarm that learns the frequency of a factory remote, but there are many factory keyless interface alarms...

Among them are the DEI Hornet 700T, the Omega AL-100H, and also the Audiovox Pursuit PRO9232 add-on alarm systems.  The AL-100H is available for not too much on eBay for only $20 US + shipping (or $40 BuyItNow + shipping)...

my year is 2001.......i am trying to get a ford alarm working on it but having problems with it self arming still and no horn chirp.

i can arm and disarm with the factory remotes..but if i disarm the system....1 minute later it arms again. the horn blows when disarmed and when triggered but not when armed.

both switches are in the correct position inside the module. its a system 4. maybe the module is bad? ive tryed the fax back system to no avail. any help??