>  If I see smoke and hear a bang I will know that you mean business.

You could also put a small steel plate in line with the coil to monitor current 
- the mag field will pluck it like a speaker. Tune for maximum sound rather 
than maximum smoke! (It would be worth putting a small permanent magnet on it, 
or it will be pulled by both half cycles and will sound at just under 18kHz, 
higher than most adults can hear.)

73,
Chris G4OKW