Heatspex were a type of goggles that allowed the wearer to see heat signatures. Vulaada Klam used a pair of the goggles to see through the fog in the lower levels of Milvayne. Chelli Aphra borrowed a pair of heatspex after meeting Klam.
Chelli Aphra wearing heatspex
Residents of the Milvayne underworld used heatspex to see through the heavy fog that was dumped there by bloatbarges. One of them was Vulaada Klam, a war refugee who had been dumped into the underworld for faults in her parent's faulty records. After the criminals Chelli Aphra and 0-0-0 were forced down to the underworld from the top city, they made a deal with Klam for transport on her Qaberworm Gurtyl, and Aphra borrowed one of her heatspex. She continued to wear it up to when she was "sold out" to the Milvayne Authority by Klam.
Heatspex first appeared in the canon comic Doctor Aphra (2016) 27, written by Si Spurrier, illustrated by Emilio Laiso, and released on December 12, 2018.