We have child locks on some of our doors already. They are lever door handles and for some reason they dot work very well, he can still open them most of the time. The alarm is a bit iffy because he could still have a chance of just runny after it sounded. Maybe one of those slide locks not sure what they are called but the ones that are in hotels lol.. We couldn't use that for the door of the patio though. Hmm
I'm sure you can find one at a hardware store. The old fashioned chain one would work.
We had lever door handles on all our downstairs doors. Those locks don't work at all, we ended up just buying a bunch of cheapy knob ones at lowes and switching them out. I'm not sure if I'll put the levers back on when he gets older, I kinda like the knobs better.