Unsure about the internal sensors, but how about a digital monitor that has a small remote sensor on it that sits in the water. The actual display/meter is attached to several feet of cord on the remote sensor and can be mounted out of sight. They are small and unobtrusive, easy to install, and you won't have to modify or touch your canister in any way..
Coralife Digital Thermometer
I used one for a while and worked fine. Replaced with a Hanna ph/temp monitor.