FORD:
No Antitheft, stuff just won't work right if not programmed correctly.
GM:
THEFT LOCK on radio screen, the radio has a VIN in it that isn't the same as the vehicle being upgraded. Like when our OBD Genie flashes red 13 times. Other VIN already present.
FCA (Chrysler):
Antitheft CODE system. The Serial number of the radio unit is used to decode the radio's antitheft code.