My son was a toddler and acting up in the store, so I grabbed him (kicking and screaming) and hauled him out to the car. I beeped the doors open with the fob attached to my purse (with a carabiner), opened the front driver's door and threw in my purse so I had both hands free to deal with my toddler... I was so mad that I put too much force when throwing my purse and it flew on the passenger seat and actually bounced off onto the floor. I slammed the door shut with my hip and went to open the rear door to throw my kid into his car seat.... it had been an epic tantrum and I was about done with dealing with it in public.
You guessed it. The force of my purse bouncing on the seat hit the fob just right and had locked all my doors. And I never heard the click over the noise of a toddler tantrum.
I had to wait 2 hours for my uncle to bring the spare set LOL. About 5 minutes after we got locked out my kid exhausted himself and fell asleep for the whole thing. Thankfully we were at a store that had an outdoor lawn section so I sat rocking him on a lawn swing until help arrived :)
All our vehicles got a Hide-A-Key after that experience.
Unfortunately each car is slightly different so trying to FIND the Hide-A-Key when you need it is a challenge...