I had mice in my attic last year and ended up rigging a camera and light so I can monitor the traps (pain in the butt going up there). I'm hoping that the flashing and other roof repairs I did this year will have blocked whatever hole they got into, but just in case I'll be putting more traps.
I decided to go with a different approach and have it send me an email when the traps trigger.
Basically this will connect to my arduino based environmental monitoring device that I made. So when the traps are active it completes the circuit, when they get deactivated it will break the circuit.
There will be an ethernet port on there and the cable that runs up the attic will have an Ethernet end so I can easily disconnect and bring the whole thing down to discard the bodies when I do catch any. I still have to finish coding the environmental monitoring app but for now I can use an ohm meter to check.
Hopefully I don't catch any, as that will mean the problem has been fixed, but with this setup it will be a long term monitoring that I can set and forget.