The ELT is a box-like device used to signal Superman.
At some point, the ELTs were designed as a means to signal Superman, with one being given to Lois and her father General Sam Lane each. Sam Lane used one when a nuclear power plant near Metropolis was overheating, alerting Superman and allowing him to prevent the disaster.
When Jordan Kent began displaying Kryptonian powers, he asked for an ELT in case of emergencies. Though he received one, Clark reminded him that ELTs weren't the solution to his problems. After a bonfire that resulted in Tag Harris gaining powers through Jordan's accidental use of heat vision, Jonathan urged Jordan to use the ELT to alert their father, who was busy apprehending Thaddeus Killgrave.
Lois used the ELT to get Superman's attention when Jonathan was trapped in John Irons' RV.
Emily Phan came to the Kent Farm, seeking to harm Lois, but as Lois reached for the ELT to summon Superman, Emily grabbed it first and, eventually, gave it to Morgan Edge, who used it to call Superman so they could talk.
Later, Morgan Edge used again the ELT of Lois to call Superman and talk to him more but he also used it to call his Subjekts to fight Superman, but they were all neutralized by Superman who tricked the Subjekts to fire their heat vision into the Eradicator along with his heat vision to power it and revert them back to normal.
- Signal frequency: The ELT's main purpose is to signal Superman during emergencies, emitting a specific frequency that he can hone in on. However it later became a trigger frequency that Morgan Edge used to call his Subjekts to fight Superman.
Superman & Lois
- The ELTs seem to be a new version of the signal watch, which served the same purpose.
Behind the scenes
- The ELTs are likely adapted from the Justice League International's transmission device, sporting a similar look and being used to communicate with the Justice League. In the DC comics, the transmission device has gone through various different looks, first debuting in The Brave and the Bold #28 (March, 1960).