I recently snagged the Surface Pro 4 keyboard that comes with the new Fingerprint ID that works with Windows Hello and logs you into the device using only your fingerprints. The new, updated keyboard actually works with the Surface Pro 3, too. The enhanced keyboard makes typing a much better experienced due to its redesign and, in most cases, will be a worthy upgrade for a Surface Pro 3 user. Read about it here: Two Reasons You Might Want to Upgrade Your Surface Pro 3 Keyboard.
The Fingerprint ID is a neat feature for this particular keyboard, allowing you to login using only your finger. Obviously, this feature is most important for the Surface Pro 3 since the Surface Pro 4 comes with the special cameras to allow login by facial recognition. However, setting the Fingerprint ID up is the same process for either Microsoft tablet version.
Follow through the gallery above to get the steps for setting this up.
Additionally, if you need to troubleshoot one that's not working, use this link: http://surface.com/fingerprintsetup
There's two versions of the Surface Pro 4 keyboard. One without the Fingerprint ID and one with it:
Surface Pro 4 Keyboard ($129.99)
For those using a Surface Pro 4, the ID-less version is good enough.