Seeing through walls and knowing clearly what exist inside just like a superman are not only fantastic wishes for humans, but also of much practical significance. For example, you would like to know whether there are pipes, or rebars inside a wall before drilling into it. Moreover, knowing how pipes are configured in a wall before attempting to fix defects would definitely prevent unnecessary damages. Existing methods that intend to address this issue are either costly due to the use of high-end technology, or restrictive for reasons of some strong assumptions. However, in this paper, we present a novel system, SmartScanner, which is based on off-the-shelf sensors embedded in a smartphone. SmartScanner makes full use of in-built sensors, namely, the accelerometer, gyroscope, and magnetometer to achieve this goal inexpensively and conveniently. Specifically, by combining these sensors, we are able to clearly distinguish certain objects inside a wall and map out the layout of an in-wall pipeline system.We implement SmartScanner on two smartphone platforms, namely iPhone 4 and Xiaomi Mi2S, and conduct extensive experiments to evaluate its performance. Experiments show that SmartScanner can achieve high accuracies in distinguishing objects in various scenarios. Meanwhile, as for layout mapping, 90 percent of length errors are limited to several centimeters for horizontal and vertical pipeline segments, respectively. Also, SmartScanner can achieve centimeter-level position errors of turning points in horizontal and vertical directions in the testbed. © 2015 IEEE.