Mission Possible/Bimetallic strip

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A coil of bimetallic strip
A bimetallic strip is composed of two different kinds of metals that have been bonded to each other in a strip. Since the metals react to changes in temperature differently, the strip will curl in one direction or the other (or curl and uncurl, if it is formed into a coil). This can be used to make a transfer that reliably reacts to changes in temperature.


Any digital device is likely to be using a thermistor or thermocouple to detect changes in temperature, not a bimetallic strip, so analog devices are your best bet for finding these.


The common rotary dial analog thermometers use bimetallic strips that are formed into a coil. One end remains fixed while the other end controls the dial's movement. The common outdoor dial thermometers, oven dial thermometers, and hopefully any other rotary dial analog thermometer should have a coil of bimetallic strip in them. Shouldn't cost more than $5.

Outdoor Dial Thermometer Breakdown

Original thermometer. Sometimes the coil is hidden on the back
The coil, removed.

Oven Dial Thermometer Breakdown

Original thermometer.
The disassembled parts.
The coil on the back of the dial.


Analog thermostats may contain bimetallic strips (more than one, potentially). There is also a good change that any given analog thermostat will use a mercury switch (mercury counts as a hazardous substance both in Mission and real life, so either don't even mess with it or be darned careful).

Thermostat Breakdown

Main bimetallic coil. This is what trips the mercury switch.
Secondary bimetallic coil. This is the marker for the current temperature readout.


  • Cooling - it is usually easier to cool the strip down to ambient temperature from a higher temperature