I just mocked up a Radio Shack piezo buzzer today figuring that sound is better than a light. It works okay, but I'd like it a bit louder. I picked a buzzer with low current draw (about 10 mA I think), but it's only about 75-85 db, so you can hear it but it's probably not loud enough to hear it easily on the road course with the windows down and my helmet on. The higher db buzzers (like what you'd find in a smoke alarm) all consumed a lot more amps. Anyone know what is a safe? Would 100-150 mA be too much?

 

You'll need at least a 105- 110dB buzzer to hear it well enough while in a WOT condition. I would try and keep it under 100mA at the most. I have no idea what the output circuit in the ECU is capable of allowing.

The safest bet is to use a transistor to turn on the buzzer.