An RFID door lock for you and your roommates, notifies others when someone gets home (with a little tune in MP3 shield or with text messages)
My roommates and I move around every 4 months thanks to our coop/school schedule. I became a little concerned over the number of people who had the same keys before us ( 5 people * 3 terms a year = 15 every year). Changing new locks every term is unrealistic. I came across these magnetic locks that are really easy to install. So why not use an arduino and use RFID tags to unlock the door?
Every roommate has an unique identification code and their corresponding RFID cards. They can use their card to unock the door, which sends the homeowner a text on who has arrived home. Alternatively, plays a corresponding mp3 audio for the user
Use your own keycode, use your own ID code, place your circuits behind the door and hide the wires xD