Bluetooth Smart, also known as Bluetooth Low Energy, is a technology that is an optiional part of the Bluetooth 4.0 specification. As its secondary name suggest it uses less energy than a traditional Bluetooth connection, thus allowing for the possibility of always-on connections.
Bluetooth Smart capability is already available on the the Lumia 925 and Lumia 1020, and is being added to existing devices as part of the Lumia Amber update that ships with the Windows Phone GDR2 update. The Verge suggests that the new accessory will be officially announced by Nokia one the Lumia Amber update starts rolling out. We'll post in more detail about the accessory once that happens.
As we have previously explained Bluetooth Low Energy is not really distinguishable from traditional Bluetooth except in the use cases it enables:
For consumers there is little visible difference between Bluetooth Low Energy and "classic" Bluetooth. On the software user interface side Bluetooth Low Energy devices are usually connected and managed in the same way as "classic" Bluetooth devices. We would expect Windows Phone to follow the same pattern with such devices handles in the Bluetooth module of the standard Settings app.
Mobile phones and computers that support Bluetooth Low Energy are described as being Bluetooth SMART Ready and accessories using Bluetooth Low Energy are branded as using Bluetooth SMART. Bluetooth SMART accessories will not work with device that only support "classic" Bluetooth.
The importance of Bluetooth Low Energy support in Windows Phone is that there are an increasing number of accessories that support the technology (e.g. Fitbit Ultra, Nike Fuelband) and many more are likely to come on to the market in the next year. In many cases an additional app may be required in order for the Windows Phone device to take advantage of the accessory (e.g. a Fitbit Ultra would need an app that supported connecting to and receiving data from the device by Bluetooth SMART).
Here's how The Verge describe the forthcoming Nokia accessory:
The basic idea is to let Windows Phone users track items with a special application and the small square Treasure Tag accessory. Tile, a recently funded Kickstarter project, is very similar in concept to Nokia's device, and works with Apple's iPhone. Nokia has built a Treasure Tag application for Windows Phone that will let users manage the sensor and locate it when it's lost. The app will also display the location of the sensor on a map, complete with Nokia's LiveSight augmented reality view. You'll also be able to locate a phone that's paired to the sensor by holding down a key on the device. The sensor will trigger a notification sound on a phone, but only if it's within range.
The Verage also note that the "treasure tag" accessory is expected to be just one of a series of Bluetooth Smart accessories from Nokia. We would also anticipate that third party Bluetooth Smart accessories will also be made compatible with Windows Phone (i.e. enabling apps for things like Fitbit will become available).