Instructions
Purchase the minikit detector once you have unlocked it by obtaining the power bricks. The costs vary from game to game -- 250,000 of the studs currency in "Lego Star Wars" and 300,000 studs in "Lego Batman" -- and the location at which you buy items also differs by game. Check your game's instructions to find the proper location.
Obtain a minikit detector with a cheat code. If you prefer the easy way you can use codes in some games to get this device. In "LEGO Batman" enter the code "ZXGH9J" at the Batcave computer to get the detector for free.
Enter a stage in which you have yet to collect all of the minikits. Your minikit detector will display flashing arrows pointing at locations with minikits you have missed in earlier travels.
Use objects in the environment to find the minikit if the location of the hidden item is not obvious even with the flashing arrow. You may occasionally have to destroy objects to uncover minikits, or build tools such as ladders to reach a minikit.