Since urine gives off a fluorescent glow under ultraviolet light, a blacklight can be a useful tool for locating areas of rat contamination. Rats keep indoor runways, or well-used paths, free of cobwebs, debris, and dust. Norway rats' runways are usually well-defined paths at floor level next to walls and other vertical surfaces. Roof rats' runways are above on rafters, pipes, etc. Outside, roof and Norway rats' runways appear as narrow paths through vegetation.
Rats make sounds when climbing, gnawing, clawing and moving.
Footprints and tail drags can be seen in dusty locations. Use notoxic tracking dust such as talcum powder or flour to determine if rodents are frequeting certain areas. Gnaw marks are a sure sign of rats. On wood, the older the gnawing, the darker the wood. If dogs or cats unexplainably get excited, rats are probably moving about in walls voids or ceilings.