Abstract: A sensor unit for attachment to a container such as a bag or other vessel used to retain material includes a clamping mechanism for attaching the sensor unit to the container. The clamping mechanism may be configured to break or provide an indication that the connection between the sensor and container has broken that is visually detectable before a leak of material occurs or is detectable by a person visually monitoring the container or sensor. Such an indication can also indicate that the sensor was previously used and should not be used again for single use applications. Such a visual indicator is separate and different from seeing an actual leak and permits an event that may desterilize material within the container or lead to other problems to be corrected prior to use of a single use reaction system.