In the prehospital setting, EMS providers usually use many kinds of medical devices on daily basis. The devices do work in the field? Most of medical devices were developed and tested in the hospital setting, stable, bright, and secure. But the EMS field is different. It is so unstable, dark, and fragile. So EMS providers need medical devices fitted to their own setting. In this lecture, I will review current status of EMS devices using in the field, and suggest point of improvements and new idea.