When I went out to the parking lot tonight, Model S wouldn't let me in. I pressed the handles, waved the key around, nothing. I had to unlock it from my phone. Luckily it wasn't pouring rain or a blizzard, just cold. Got inside and it wouldn't let me start: "Key not inside car". Bah. Had to start it from the phone. It's less than 4 months old, shouldn't have a dead key battery yet. It never warned me about low battery. Got home, removed the battery, measured it: 3.0V. Took my second key fob (which I've never used) out to the garage, the handles presented properly. Replaced the battery in the 'bad' one with a fresh CR2032 and went out, same. Put back the 'bad' battery, went to the garage, and the handles presented. So I don't know what it's problem was earlier.