KJT-SJ non-contact digital slip detector is an economical, reliable, simple and versatile monitoring device for shaft speed and other rotating devices. When it detects that the current speed signal is lower than or higher than the normal speed range, the switch outputs a set of switching signals for alarm or shutdown. No moving parts, no wear, long safety life, integrated structure, centralized control device, simple setting or troubleshooting. The shell adopts a waterproof and dustproof design, and two bolts fix the shell, so it can be directly installed and used in harsh environments.