There exists "alternate data", some companies monitor all kinds of stuff, satellite pictures, etc, some of these companies surely saw the inevitable asset positioning just before such a big attack (150 planes).
Just like the Ukraine invasion was first visible on Google Maps as traffic jams !!! at the border at midnight
https://www.washingtonpost.com/technology/2022/02/25/google-...
You can also do entertaining things like determine if a factory/data-center is running at full capacity by looking at the fans in the cooling stacks. Satellites take the red, green, and blue channels separately at different times so you can see if a fan is spinning through the apparent chromatic aberration of the blades, same deal with anything else that spins or moves. If you know the satellite you're buying imagery from, its TLE and a little information about the sensor you can work out all sorts of fun details.
Just look at the lead up to the Ukraine invasion, the US intelligence services were practically screaming from the rooftops that it was happening. Russians were obviously stacking up on two borders. Meanwhile, reporters were on the street asking people how they felt about the oncoming invasion and they all said some variation of "they've been threatening that forever, it's all talk, it won't happen".
The Ukrainian government took the approach of not starting a full on panic. They thought maybe there was still some chance of stopping it. And not knowing 100% the day and time meant stopping the economy, people fleeing and such. It could even play into the hands of the enemy as they could react and postpone as well.
Some have criticized the government for that tactic science. Some might say they should have listened to the US intelligence instead, but that presumes people should trust the US intelligence more than their own government.