OK, this is a hack of code Cronel has on his snippets site, which allows players with the skill to listen for sneaking hiding devious invisible things in the room they're in, or in a direction they specify.
Because there's already a do_listen function in 1.60b, I had to tweak it a little to get it to work, so here it is. I removed the success train functions, changed it to bypass the problem with listen already existing for the channels control, and fixed some of the function calls to match AFK's setup. The original code can be found here.
I moved the code to my new snippets page, to make it easier to read. You can get it from here