I vote waste of money. If your engine is detonating, you will hear it and feel it. No sensor needed. 11:1 with aluminum heads (?) should do alright on 93 octane I would think.
I agree. And they give so many false signals that they aren't accurte by any means. 11:1 on 93 is the limit though and you need to know the quality of the fuel. The stuff from some of the stations gets it octane with a healthy dose of alcohol and it ain't the same as good 93 octane gas. Sunoco Ultra 94 is good if you can get it. Of the 4 Sunoco stations in my town only 1 has Ultra 94 now. The rest stopped carrying it and switched their pumps to diesel.