Recently saw on TOH a device that would shut off the water supply to a hot water heater via a float in the drip pan below in the event of failure. My question is even though the water supply is off, the contents of the water heater could drain leaving it empty. What is the result of still having the heating soure (gas or electric)still active. Is there a risk of fire if left unattended after the water tank is empty, and if so, how long.
I want to install shut-off device at both of my places. Also travel alot and concerned about the fire danger.
Any and all help would be appreciated.

Dave Richards
Reno , NV