GE Personal Security Door Stop Alarm
Set this under your closed door at night, and if anyone tries to open the door it sounds an alarm and stops the door from being opened fully.
This is great for dorm rooms or apartments! Just don’t activate it before your roommate gets home.
One thing to consider–if your doors have a big gap or no gap at all this item may not work, but for the price you can take it along to your next place.