More to explore:
Door Handle w/Safety Lock - http://www.thisoldhouse.com - On the door's knob or on the plate around it, there should be a small hole that's made for unlocking the door. Take a slim piece of metal, such as a small flathead screwdriver, and slip it in the hole. Compress the spring inside or slip the screwdriver head into the slot on the spring and turn; door unlocked.
47 skills for around the house
47 Skills You Need to Survive Homeownership. This is one reason I only buy door knobs with skeleton keys...
Pin now, read later: 47 things you need to know when you own a home.
16. Pick an Interior Lock | 47 Skills You Need to Survive Homeownership | This Old House