Step 8 - The final step is to add Redstone Dust to the untouched block on the right hand side, then run it where you need it to go.
What this will do, is create a system where you can create a Puzzle for your adventure map or server. If you have three of these Block Update Detectors running into a 3 Way Inverter that inverts the signal when a signal is ran into it.
When all three blocks are placed in the appropriate color coded places, the Invertor will allow the signal to continue, thus allowing you to open then door or secret passage way.
As you can see, this is extremely useful for both a Server and an Adventure map. You could even use it in your own map for a little bit of fun in your letsplay series.
On the next page, you'll see an image of what it looks like to color code the Block Update Detector.