Interesting premise. Reminds me a little of 'Hunt the Wumpus' (a game developed by researchers to talk about Artificial Intelligence).
I like not restricting players with uses of the echolocator. It would be a good challenge to include a counter of how many times the echolocator was used, however. If you need a motivator for players to try using it less often, all you'd need is a 'good ending' and a 'neutral ending'.
Have you considered letting the monsters move? Of course you'd have to dim the tiles as the information they contain get less certain with the moving monsters (and possibly walls too?)
There is lots of potential with this game!