I believe many creators would like a fire alarm block with different light colors and tones like on a Gentex commander alarm (beep beep beep, woop woop, buzz buzz), etc. plus a fire sensor to activate the alarm. A flood sensor that outputs when touching water would also be handy so that you didn't have to figure out the volume of your creation, divide that, wire it up, and add logic to detect when water reaches a particular block. It would also be very useful for detecting when your sub was underwater. Thank you for taking your time reading this suggestion, Sprock3t.
P.S. A smoke detector would work well for the fire sensor, plus smoke would make the game more realistic
P. P. S. Maybe fire sprinklers with multiple spray types (pipe top mount, ceiling mount, wall mount) that activate when it gets too hot.