I had been having thoughts about a small Arduino on the sled which would have an accelerometer to aid in accuracy and tilt detection. But with the small fire that started, I realized that fire detection would also be easy using a small contactless IR detector. This would be great to avoid fires… In the event of the bit becoming too hot, it could pause or shut down the machine before a fire started.
As a quick and dirty alternative, I also started thinking about how a brick could be replaced with a pressurized water bottle. Modify a cap, add bubbly water, a metal straw, and crimp the end around something that melts away in the event of a fire (like a healthy bit of hot glue?).