I have a yard customer I’ll call Maureen. She has a daughter age 47, named Adelaide; a granddaughter who will be 18 in July, and a six-year-old grandson named Bert. Bert’s mother was apparently so lacking in parental discipline with this third child (she has never married) that she didn’t even toilet-train him; just about everything had to be done by the grandmother, who is already 70. The daughter doesn’t do a damn thing. I’m not kidding.
The specific problem I’ve faced when I go over there to do housework, yard work, or other chores for the family, is getting out the front door. The grandmother had a key lock installed on the inside of the front door (no other door opens onto the front yard; the back has a high fence around it) so Bert couldn’t go outside; she had even put a “leaf” lock on the door, that you lift and turn to the right or left to lock or unlock. Is there any other way to do this, short of keeping that kid in a cage? :o :mad:
Well, first of all, that’s an extremely dangerous situation: doors locked on the inside are a death sentence in the event of a fire or gas leak.
OK. It sounds like what you really want/need is a key. If she’s not willing to let you have a key, I can’t think of anything that will let you out and not let the kid out.
Ok, you could move the doorknob up to the top of the door, so that he just can’t reach it, but that’ll only last until he discovers chairs.
Truly expensive solution: electronic lock on the inside - everybody gets a “clicker” but Bert, and the clicker gives you 5 seconds to get out the door before it locks.
Is this a double cylinder deadbolt (A dead bolt that takes a key from both sides of the door). Easy way it so ask for a key. Besides if the door is locked to keep the heathen in someone should be locking it back after you leave.
While I shall not be an alarmist such as Nametag, these locks do delay and can potentially stop someone from leaving in case of a hazard. (they are illegal in only two of the 50 States California and Indiana.) A key kept on a hook or peg out of reach and sight from the child yet accessable to an adult in need of exit.
There is not really many(realistic) options, A deadbolt or some form of latch/bolt/hook lock out of reach of the child.
Oh another option is try to find a door chime, they make electrical ones that attach to the wall and a magenet to the door, when the door opens they buzz or ring. This will at least give someone a heads up that the ruffian is on the loose and making a break.
Best of luck… if nothing else works maybe duct taping some oven mitts over his hands would work? 
just kidding
You might like this page, it has 48 childproof locks under $10:
http://www.epinions.com/kifm-Safety-Household_Precautions-All-Price-0_to_10
Psssssst. The OP is in California.
I’ve seen “child-resistant” doorknobs - they work along the lines of medicine bottle caps - you need to squeeze tabs, push and turn or do something similar that’s presumably difficult for a child’s hands to do. Otherwise, the thing spins freely and doesn’t engage.
If they’re using a double-cylinder deadbolt because of glass near the door, they should consider changing the glass to Lexan so someone can’t just walk up, break the glass and reach in to open the door.
At Lowes they have door lock with a 10 key keypad. Punch in the code and the door unlocks. Now it’s made to have the keypad on the outside, but it may be workable.
Still doesn’t solve the fire exit issue though.
The door has a “fanlight”–a protractor-shaped window, in several segments, at the very top. I’m 6’2" and I can’t see through the window, let alone Bert.
Apparently he found out how to slip the leaf-lock, a brass piece, up and away from the edge of the door. I wonder if there’s something weight- or voice-activated, that could keep him from opening the door.
I have several times urged the grandmother to go to a lawyer to deal with her daughter, who even steals from her. 
But the grandmother has no relatives living in California whom she could leave Bert with–he goes to school on a half-day basis in the morning, and her daughter and granddaughter cannot be relied on to look after Bert while she takes care of other matters. There’s only so much I can do…