I can only agree with the players here that already said that there is no neccessary to add another lock or pin generator in the game. I guess everyone makes this mistake only once and is more careful after that (Support usually helps player to get their monster back one time).
As a Mum i can say - secure your device and dont let little children play with it on their own, cause they might do worse things then selling a monster in monster legends.
But, if you need a solution:
That might also be helpful for those who agreed with you here.
In my opinion there are much more important things to fix/add in the game were SP is/should work on.
Edit: live links, per forum rules
Playing Monster Legends since January 2015 - still having fun and addicted😁
Co-Lead of Top-Ten Team Five Attacks