One of the more exciting features in Apple's upcoming OS X Yosemite is the Handoff feature that allows a seamless app transition between your Mac and iOS devices.
The feature, however, is based on Bluetooth 4.0/LE which was first introduced in Macs in Mid 2011. The feature has since made its way into later Mac releases, finally coming to every Mac as of the 2013 Mac Pro.
Apfeleimer has published this chart which shows all Macs that support Yosemite, and the subset of those which have support for this version of Bluetooth:
The full bars represent Macs that can run OS X Yosemite, while only Mac models in the green bar timeframes support the required Bluetooth protocol for Handoff. For iOS users, the iPad 2 is the only device that is capable of running iOS 8 but doesn't come with hardware support for Bluetooth LE. While Apfeleimer expresses some uncertainty in their article about this being an absolute requirement, in the WWDC sessions, Apple clearly states that Handoff runs on Bluetooth LE technology.
OS X Yosemite is in developer beta right now and will be released to customers later this year.
Article Link: Yosemite 'Hand Off' Feature Limited to Macs with Bluetooth LE