Week one, Instructables. Arduino discovery

http://www.instructables.com/id/20-Unbelievable-Arduino-Projects/

This page was a stepping stone for understanding the capabilies of arduino. We discovered lots of simple arduino constructions that we could possibly make ourselves.

http://www.instructables.com/id/Secret-Knock-Detecting-Door-Lock/

 This in particular I enjoyed. It seemed to ring true with the 'inputs/outputs' thing.
Input- secret knock
output- door unlocks.
Simple and yet a very good idea. It offers privacy, security..... if this idea were to be refined and developed this could be a very useful legitimate design.
For example, you don't come home form work until 5 and the kids come home at 3. Kid forgets key/ hidden key is left inside house. The kid can call up mum and ask for the secret knock so they can get in.

How one would program this is still a mystery but it seems to me to be one input/output which seems to be simple.