PATS is Passive Anti-Theft System, its not an "alarm" its passive, which means all it will do is disable the fuel injectors unless the correct key is used in the ignition, no horn honks or lights flashing just no start
Also known as Ford Securilock
It can also disable starter motor and fuel pump, but these are easy to by-pass, can't by-pass no injectors
PATS was optional in Ford models starting in 1996 Mustangs
In Rangers 1998 was optional and 1999 V6 and up it was standard equipment
Until 2001 PATS was a separate module, above glove box in Rangers, it was connected to the V6 engine computer and the computer would not pulse the fuel injectors unless PATS module gave it an "OK to Start" message
PATS keys have a black plastic handle with an RFID chip(transponder chip) embedded inside
The ignition cylinder would have a Ring/antenna around it, called a transceiver, when the key was turned on the PATS module would read the "chip" unique number, and compare that number to the 3 or 4 numbers(keys) that were programmed in at the factory
If it found a match, engine could be started, no match and no start
If you are changing computers, like in a V8 swap, then you will need to know if the new computer requires PATS "OK" to work, which is by YEAR of computer
PATS module and computer at "matched set" so you can't just swap in a new computer, programming is needed
If new computer doesn't require PATS then, in a Ranger, all you need to do is to Ground the Starter Relay in the engine fuse box to restore Key Start