Most of the internal doors in our house are the thin easy to break down variety. Hubby is concerned with security, especially when he’s away for army stuff, so we have been installing safety measures. All the bedrooms have locking doorknobs and our master bedroom actually has a deadbolt since the door has latching problems and otherwise is too easy to push open.
I realize it sounds weird to say our master bedroom door has a deadbolt but for whatever reason the doors that came with our house are cheap and don’t always work right. We had to install a deadbolt on the internal garage door as well because of latching issues. Once on a particularly windy day we got a call from our alarm company that the alarm was set off. Well, the wind was so strong that it pushed that internal door open and set off the alarm. So we installed a deadbolt to keep the door always latched. We figured the same idea would work in our bedroom.
We’ve also discussed the possibility of replacing those doors someday with more sturdy and stronger doors. I found this interesting article called How to Replace an Interior Door that has some good tips and ideas. It does sound pretty complex since it would require modifying the new doors purchased to fit the size of the frame and it would also involve chiseling out hinge areas. That leaves a possibility of messing up and having to buy a new door to work with, and they are not cheap. But it is an idea to discuss for future home improvement projects.