Someone showed this on one of the threads and I got one. It's not for outside but works well in the attic like you describe. If you use it in a place like an attic where you can't see it, you can get a "rat tale" with it that plugs in and has an extension so that you can place it where it can be seen if the trap is in an obscure place.
I DID use it outside but I put it in a rubbermade type container and cut an entry. Worked well and caught mice in the run during the winter. Also caught chipmunks in the garage while I was separating a bird out in there. So far I've never had any in the chicken house. Expensive (you can find them cheaper than this link) but no poison or snap traps around the chickens or other pets made it worth it to me. In the winter I was catching mice in the run EVERY time I set it.
http://www.amazon.com/Rat-Zapper-Ul...TF8&qid=1400980481&sr=8-2&keywords=rat+zapper
I was hoping it might handle a weasel if we had any but so far I haven't seen one.