I saw a press release about a device called the TxtStopper, which is a cell phone jammer you wire into your car's 12v power line to jam cell phones when your engine is running. The idea is to keep your teenager from texting while driving.
This device is probably not legal in the U.S., since it interferes with legal and regulated cell phone signals.
Also, I don't see how they keep it just to your vehicle. If it is so low powered that it doesn't extend much beyond about a 5 foot radius, it may not be powerful enough to reliably jam your phone.
Also, cell phones in vehicles have legitimate safety uses, such as 911.
Bad idea.
