Good grief, all you have to do is interrupt current in the primary circuit when the door opens. The conducting path for the primary is between the door frame and the door hardware. The secondary (HV) side attaches to the doorknob on the inside. When you expect your roommate, you simply energize the primary with a hefty battery. The door frame is circuit 'common.'
You could do it with a 555 and a transistor. I once made a friend an electric fence driver with an old valve radio transformer and an ignition coil. On one half cycle the HV winding charged up a cap. On the next half cycle the 6.3v winding triggered an SCR which put the cap across the coil. You just had to get within half an inch and a spark would jump across onto you. My friend was called Frank, so we called my device Frank's Zapper...
There are a few details missing here, since, in the era that he plated this trick, automotive ignition coils did not include any interrupting means integral with the coil assembly. So we could assume that it was probably one of the very old Ford Sparking coil devices. If not, then it could be useful to know just how a more current coil was driven to work in this application.
The innovative application of a mix of simulation techniques has provided a team at IBM with a unique ability to view the connection between atomic bond type, drift and electrical conductivity in PCM devices. Results overturn some old ideas of band gap expansion.
Wide band gap semiconductor materials (diamond, silicon carbide, and gallium nitride) are well positioned to play important roles in the next and future generations of consumer and military/defense electronics capability.