The user-programmable model: this machine allows the car owner to enter a secret byte into a register. the user selects a byte using two hex keyboards, and presses an entercode pushbutton to store the code word. now when the machine is used "in the field", the car owner enters a sequence using the same pushbutton arrangement as for the previous machine. when the sequence so entered matches the code word stored in the register, e goes high. as with the factory preset model, if more than 16 bits are entered without the proper sequence being observed, the system shuts off (until reset is pressed).