Yes, plumbers can detect leaks behind walls using specialized tools and techniques. One common method is to use a moisture meter to detect elevated levels of moisture in the wall, which can indicate the location of a hidden leak. Plumbers may also use infrared cameras to detect changes in temperature that can be caused by water leaks. Another technique is to perform a pressure test on the plumbing system, which can help identify leaks and other issues. However, accessing the leak may require opening up the wall, so it's important to hire a licensed and experienced plumber to minimize damage and ensure proper repair.