This probably falls under both Apps and Accessories, but one technology that was shown at the MWC was the Stick n Find. The Stick n Find is uses bluetooth radiotechnology to locate missing items. This includes keys, wallets, etc. I understood that if these items get separated from you, a buzzing sound is set off and your smart phone is able to track them. This is something that could've really come in handy for me during my college years!! Here is some more info:
The first function the app offers is a simple radar screen that approximates the distance - but not yet the location - of all the paired Stick-N-Find stickers in range. The technology does not yet allow the app to determine which direction the lost items are in, so users have to start walking while watching the screen to see whether the device they are hunting for gets closer.
That article is from December but I first found the app on the best of MWC highlights. I hope new technologies serving as tracking devices start coming around more!