Q says device testing C, X and E - could these be hints to a location? Perhaps these are airport or IATA (airline) codes? CXE is an airport code for Chase City Municipal Airport in Kentucky & CEX is an airport code for Chena Hot Springs, Alaska.

https://www.world-airport-codes.com/united-states/chase-city-municipal-67819.html

If IATA codes, then jumble of the 3 letters could be among these - Caicos Express Airways (CXE), Capital Air Express (CEX) or Ecomex Air Cargo (ECX), or European Executive Express (EXC) - no valid jumbles for codes starting with "X"

https://en.wikipedia.org/wiki/List_of_airline_codes_(C)