Nokia is preparing to launch a proximity sensor accessory for its range of Lumia Windows Phones. Sources familiar with Nokia's plans have revealed to The Verge that the Finnish smartphone maker will debut a "Treasure Tag" accessory that combines Bluetooth 4.0 and NFC to track items from a phone. The Treasure Tag will pair with Lumia Windows Phones via NFC, and Nokia will ship the device with a loop strap to attach it to a set of keys.

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.

Treasure Tag is designed to be "always on," and includes a battery that will last for around six months of use. Nokia is updating its Lumia Windows Phones with Bluetooth 4.0 support, and the Treasure Tag will be one of the first accessories to make use of the new Low Energy support. We're told that Treasure Tag will debut in the coming weeks, once Nokia starts to roll outs its Amber update that includes Bluetooth 4.0 support. We understand that Nokia is also planning additional accessories that make use of the upcoming Bluetooth update to Lumia Windows Phones.

Aaron Souppouris contributed to this report