Bluetooth 4.0 has been around for a few years now. Chances are if you've bought a new phone in the past couple of years it has been supported (everything from the iPhone 4S has it, for instance). The difference with Bluetooth's earlier incarnations is that 4.0 is specifically geared to support low power consumption. This is exciting as it means that there's all sorts of new devices that could take advantage of this - here's some of the most intriguing!
August Smart Lock
Keys are so last millenium. The August Smart Lock sits on the back of your door and interacts directly with the deadbolt. So when you get home you can simply stroll up to your frontdoor and have it unlock right in front of you - no faffing about with keys required. Similarly, when you leave the house it’ll lock the door after you. What’s pretty cool about this is that it means you can do some really clever things beyond the basic door opening and locking. For example - if multiple people in your household have the app on their phones, they can have their own unique key, so you can see when people have entered and left the house. Perhaps more crucially, you can assign temporary keys and put them on timers. So if you’re rich enough to have a cleaner, you can grant your cleaner access only for a couple of hours a week - or if you’re on the other side of the world and a friend needs to go in and water the plants, you can grant them access remotely. Plus there’s no need to worry if your phone batteries dies - you won’t be locked out as your lock will still work with a traditional key.