Scraplets have the ability to thermal scan, which can tell whether what is metal and what isn't metal. This helps them find their "meal" in a quick instant.
Scrapheap[]
The Scraplets use thermal scanning on Bumblebee, Bulkhead and Ratchet.
Orion Pax, Part 3[]
The Scraplets returned and used thermal scanning to eat Vector Sigma and the Insection.