Key Cards
When you place a card detector right click it with a key card to link the key card. Right clicking the key card detector again with the same key card activates it. Note: Comparators required for signal and multiple cards can be linked to one detector.
Burn Plates
If an entity steps on the plate they take hot floor damage, the same type as magma. (Note: in the photo, it is a 2,2 of plates, not one big plate)
Metal detector
Metal detectors are triggered when a player comes close to it with an item in their inventory that can be enchanted or is enchanted, this sets the detector off. Metal detectors require comparators.