They have carbide teeth blades as mentioned before, but I would hesitate buying expensive sawzall blades because you almost only use them for demo.
You can use wood blades to cut metal too, but you get showered in hot metal shavings. I know this because my boss doesn't seem to distinguish between wood and metal blades. Metal blades used on wood also seem to be more precise and controllable, the wood ones will get caught and hammer you from time to time if they catch a nail or hit something.
You should be using a grinder if you are cutting metal in large amounts. I'm an electrician and I wish my boss would buy a grinder instead of using a sawzall to cut metal and wire, getting showered in hot metal shavings is not that comfortable.