In Electronics world? Bipolar junction Transistors. Easily.
This led into having portable devices we have today.
Back then people used vacuum tubes for switching and amplification; of which were very expensive to run (used a lot of power when idle, while having a very short lifespan of less than 48 hrs).
I mean, vacuum tubes where phenomenal when they came, allowed first long distance calls in 1915.
Look at my phone now, fits on my hands, and has billions of transistors!
Post script: lately I’ve been thinking, what if we remove cell towers as middle men? Because nowadays privacy is somewhat dead. People have been using radio frequency for walkie-talkies even before 1st generation communication (1G) was a thing.
guyrocket