This paper presents a smart cage which consists of an automated excrement detection module, a cleaning module, a feeding module, and multiple additional sensors for a dog. In the smart cage, excrement is detected by using image processing methods and is automatically cleaned up by the conveyance. Moreover, the conveyance can also be a treadmill for the dog to exercise, with its built-in and adjustable speed function which is designed for different levels of training. However, since the smart cage is automatic, it thus operates with minimal involvement from the pet owner. Therefore, the safety of the dog becomes an important issue due to no supervision. In this paper, a dependable safety agent will be proposed to solve the safety issue while the conveyance is still in use. The dependable safety agent will monitor two kinds of information and determine whether or not to stop the conveyance rotation. The first kind is the image processing technique which is used to detect the movement of the dog in the cage, with the purpose to signal for the conveyance to stop immediately if the dog moves abnormally. The second kind of information that is used to stop the conveyance, is by detecting unusual current peaks of the conveyance with the use of a current sensor. The smart cage may become safer and more reliable through using these methods to avoid any harm to the dog.