I've seen and used these as well. They are OK, but you need to still remember to bring the key-fob. Because it does not come out of the pocket/purse nearly as much, makes it (oddly) somewhat of a PITA to keep an eye on. Example: I read one time of a guy having this on his (Ducati?) Moto and after filling up at the petrol, drove back into his hometown to the Local pub. Later, Bike no longer works, has to have the tow truck come to take him home. What happened? He left the fob on top of the petrol dispenser. He was close enough to start and take off, but as he left, he "lost" the key. But never noticed, as bike worked fine (and it was not visible normally unlike a regular key, etc). Ergo, him stranded. Expensive mistake. Moral of the story is if you don't use it, you lose it. =]

My car (a Hyundai) is keyless like that so you just need the key to be on your person. There's no technical reason why this couldn't be done with NFC on a mobile phone, but I think the excuse would be about car thefts. Modern cars all use chipped keys that are really stringently tied to dealers and car thefts have plummeted during recent years.

It's a lot more convenient than I would have guessed though, one of the nice bits that I noticed is my car lights up when I walk up to it at night. Not bright, but the LED under the mirror illuminates the ground around the driver side door. Very neat.

I think all the new Dodge models (even base trim) have keyless these days as well. Hopefully it it catches on for all makes, it's a pretty nice feature.

I think this is the app I was thinking of: http://www.viper.com/smartstart/