1.Always make sure that you have the right sized trap for either mice or rat. Insects may be taking the bait, without setting off the trigger. Using a Mice Size Glue Board around the area would also catch the insects. 3.Be sure traps are in good mechanical condition. If traps need oil, use animal or vegetable oil rather than a petroleum based compound.
Some rats can be trap shy.
They are shy of new objects and placing unset traps in a new location for a few days will increase the catch. Camouflaging the trap in a shallow pan of grain or sawdust could hide it. Place the bait in a few small placements on the top surface without setting the trap. When the rats start taking the bait, set the trap, leaving only one bait placement in the set trap. Rat traps should not be relocated once a good location is found as this will set up a new obect reaction.