Add a homemade "alarm" to your bedroom door
An interesting twist on babyproofing (kid-proofing, really), from Leah:
I am a parent of a five year-old who is blind and nonverbal, but much sneakier than you might think. As we live in an apartment, we needed a cheap and non-damaging way to keep him away from certain areas (which really means keeping us aware that he's going into certain areas.) As he can outwit doors and gates and we have no way to lock our bedroom door, the solution we came upon was simple; we attatched a set of jingle bells (the bells on a strap kind that comes with those preschool rhythm-band-in-a-box sets) to the door. If he does as little as touch it the bells ring; they are loud enough to be heard, but not obnoxious, and easy to remove.