I actually had my 15 month old son lock himself in an adjoining room in a sort of nightmare scenario. We had a conference suite which meant a regular room with an adjoining extra large conference/lounge room at the Hyatt in San Diego. The doors between the rooms were propped open, but would auto-close if you removed the door stop.

The door handles were the lever type, so he was able to walk up and open the doors going out into the hotel hallway on his own. To prevent that, I engaged the swing across latch. We were in the conference room area, and I had to run to get the phone in the bedroom. The door on the conf side where my son was swung shut, and there was no handle or key to re open it from my side. I quickly ran out into the hall with my key to open the outside door, but realized that I had engaged the secondary lock and could only open the door about 1/2".

I freaked out, but calmly called the front desk and told them my son had locked himself in the adjoining room with the secondary latch engaged. They had someone up in a few minutes, while I sat in the hall with the door cracked talking to him (he was safe and content). They came up with a tool that they can put through the opening and grab the latch. Then you slam the door shut hard and it releases the latch.

Was very scary, and ever since then anytime we have an adjoining room I will lay a towel down around the door jam to prevent it from closing. Either that, or leave the deadbolt of the adjoining doors sticking out so it can't fully close.