Well...I wouldn't go quite that far. Depends on some things. The vehicle for one; hybrid vehicles can be almost silent. Also going downhill vehicles tend to be quieter. Trucks and motorcycles, you can hear coming a quarter mile away.

Then there's the wind-in-your-ears factor to consider. When I'm going down a long hill at speed the wind is muffling the sound to my ears so much that I can't even hear my phone/GPS prompts when they go off. It's so bad that now when I know I'm about to make a turn off a fast hill I will leave my screen on to make sure I get the visual info.

I think the product shows promise. If an app is developed to work with a BT enabled phone I might be interested in owning one ( if not too expensive ). Then again I might rather just have the BT enabled sensor alone rather than an integrated sensor/tail-light. If an app is developed I want it to integrate with other apps that might be is use at the same time.