A job in a 1920s apartment building in Chicago changed how I check for gas leaks

I was working on an old gas stove there last month and my standard soapy water test didn't show anything. The customer mentioned a faint smell, so I borrowed a buddy's TIF8800A combustible gas detector as a last check. It picked up a tiny leak from a cracked fitting the soap bubbles missed completely. Now I always bring a detector to any pre-1940s building. What's your go-to method for checking old gas lines?