Siemens now offer really good intelligent, adaptive thermostats as wireless replacements for the old bimetallic strip.
From the guardian.co.uk
This takes the form of a bimetallic strip mounted on the regulating slide, and carrying the curb pins at the free end.
From the en.wikipedia.org
Harrison also invented the bimetallic strip and the rolling bearing, without which most vehicles could not move.
From the en.wikipedia.org
As the device warms, the polymer expands more than the electrode close to the cold surface, and the whole device bends like the bimetallic strip in a thermostat.