A BELL you should add a bell item that you can place on a block that’s invisible to the enemy but will give you an alert when an enemy walks on that block. Would cost around 5 gold and would be single use, would just pop up with an alert “an enemy triggered your trap” on the screen of the player who placed it with a bell noise similar to the “enemy is approaching your base” alert
Could also maybe alert the enemy who triggered it, or even expand it to give them slowness for 3 seconds or something, in which case it would need to be more expensive and they would be unable to be placed too closely together
Or you could completely disregard this concept and just add a bell some other way I really just want a bell please I’m begging