I don't know if your 3 year old is as resourceful as ours is but there are few things she is scared of. A wooden dowel would be enough to discourage most kids, but not ours. When we stayed at an 11th floor oceanfront condo this week it was a real challenge to find a way to discourage d/d from trying to escape to the balcony. I have finally come up with a remedy. At just about any walmart or hardware store you can find "First Alert" instant door and window alarms. They're very inexpensive, and are self adhesive. If by chance the kiddo gets the door open, an loud alarm sounds which will hopefully discourage (scare) the child from attempting that again and it will notify you the door is being opened. If you are afraid the loud alarm will annoy your neigbors, you can change it to a door chime sound. They are very inexpensive and work well. There are four alarms to a package.