I'm not convinced it's possible to detect the lucid state without input from the dreamer, so that may be difficult to implement, and will probably rarely work if it is. Unless you've thought of a way to detect lucidity that I haven't.

Vibration doesn't seem like a great idea to me either. It's nice to have it as an additional feature, but I suspect that it would be more likely to wake the dreamer up, rather than providing a reliable cue for lucidity. The lights are a good idea, and I recommend that sound, either a simple beeping or possibly an actual voice saying something simple like "You are dreaming" would be more useful than vibration.

It's a great idea though, we definitely need more products like this available.