If you use the scanner it sends a pulse and if you look you'll see the pulse bounce off the rocks hiding the keys like echoes. but if i understand correctly there are decoy monsters that also reflect the signal so you 'll just have to go around and check them
also, as for ending 1 i just ran to where the end of the game is at the very start bec i wanted to check it out and... ¯\_(ツ)_/¯