In locksmith terms
PATS stands for Passive Anti-Theft System, the immobilizer used across Ford, Lincoln, and Mercury vehicles. It is passive because it arms itself automatically: there is nothing to switch on. When you try to start the car, PATS checks the key's transponder against the values it has stored and only enables fuel and ignition if the key is recognized.
PATS is the brand name for the same concept other makers implement under their own names. Adding a key means teaching PATS to trust a new transponder, which a locksmith does through the supported programming method for that vehicle.
In plain English
PATS is Ford's built-in theft protection. It quietly makes sure the key trying to start the car is one the car knows. If it is not, the engine will not run, even if the key turns or the button presses.
Other brands have their own versions of the same idea. PATS is just the Ford name you will see in manuals and forums.
What the theft light is telling you
A flashing or solid theft or security light during a no-start usually means PATS is not recognizing the key. Causes include an unprogrammed or copied key, a damaged transponder, or a fault in the system reading the key. A locksmith can test whether the key is being seen and program a key PATS will accept.
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