Colliders that do not collide...

one of objects needs to have rigidbody component to send u a call :)

True, I did this, but they still do not collide when I drag piece over grid in-game. When I move them trough scene view when game is running void is called, and only if I move grid cells. If I move pieces void is not called. Of course I want it to work in-game xD I tried to set rigidbody.collisionDetectionMode to other values but it did not help...Any ideas?

I put the script on grid cells or pieces, same result.

You can't just randomly try chucking scripts on different objects until it magicly works - the collision system is quite well documented - you need colliders on both components, a non-kinematic rigidbody attached to at least one of the components, and the collision layer matrix setup accordingly.

Yeah, I have that now. I do not place scripts randomly dude. Because I have grid cells and pieces I tried to put scripts on just grid cells first, and when not worked then just on pieces (I know there is no difference for collision detection, I suspected there is some bug there). I have colliders on both components, non-kinematic rigidbody attached to one of them (grid cells), layer matrix setup is fine, they do not ignore each other.