# How to detect collision in Unity3D without rigid bodies?

The target platform of my game is mobile devices therefore I try to develop it performance oriented. It will be a strategy game so I don't really need physics in it, consequently I did not add RigidBody to my object to avoid unnecessary computations. However according to the Box Collider reference page, the collison event cannot be triggered, unless one of the objects is a RigidBody. Is there a simple way to check collision between objects other than using RigidBodies? Or can it be that I'm overreacting this performance thing and the physics engine won't slow my game down?

If you don't need the physics-simulation and just care for the collisions, why not use sensors (or "triggers", as they are called in Unity). For stationary objects, use a collider with the Is Trigger checkbox ticked. For moving objects do the same, but also add a rigidbody and set it to be kinematic.
That way you'll only get collisions out of the engine and no other simulation is necessary (use the OnTrigger... callbacks instead of the OnCollision... ones).