[robespierre]

Thermal printers are very reliable, but the ribbons may be hard to source. Unlike typical "dot matrix" impact printers, a thermal head has no moving parts. It just passes current through some wires to heat them up.
Heat releases the binder of the ribbon, transferring the black side to the paper. They will also print, without a ribbon, on thermal sensitive paper, known as "fax paper".
With impact printers, the ribbons can be re-used by dipping them in an ink-oil mixture, but thermal ribbons can't be reused at all; the negative of every line of text that was printed is permanently etched on the ribbon. This also makes them interesting for your next spy thriller novel, since the contents of the classified dox can be fished out of the e-waste basket.