There are 1512 ways.
Let ABCD be the four digit alarm code. Since the first digit must be a 2, 4, or 9, there are only 3 possible values of A. Since any number cannot be repeated, B, C, and D can't have 10 possible values. B can have 9 possible values since one number is already occupied by A. C can have 8 possible values since two numbers are already occupied by A and B. D can have 7 possible values since three numbers are already occupied by A, B, and C. By the Fundamental Counting Principle, ABCD can have 3•9•8•7=1512 possible values.