A seismometer is the planet's ear. It picks up the faintest tremors in the ground and turns them into an electrical signal. But this ear isn't perfect: its sensitivity depends on temperature. In the cold and in the heat, the instrument hears slightly differently, and that introduces error into measurements.
Japanese researchers built a test rig that shakes the instrument with a precisely controlled force while the instrument sits inside a thermal chamber — from minus 15 to plus 45 degrees Celsius. That's how they measured how the response of three seismometer models changes. It turns out that for each degree, sensitivity shifts by about 0.11%. The culprit is the magnet inside the instrument: its strength depends on temperature.
What does this mean for science? Seismometer networks blanket the planet, from Antarctica to the equator. If you ignore the temperature correction, data from different locations will be slightly out of sync. Now geophysicists have the numbers to subtract that error and listen to Earth more accurately.
The magnet in a seismometer weakens when heated, just like an ordinary fridge magnet if you warm it up.
In the movie The Core, characters listen to the planet's interior using seismometers, and any instrument inaccuracy could cost them their lives.