SpaceX received a $4 billion military contract to do this, but with radar and from orbit.

I wonder how this system can be protected from spam - if anyone can send data there, enemy can, too

Shahed drones have increased in altitude from ~500m at the beginning of the Ukraine war to 2000-3000m, which is a 4x reduction in noise on the ground. The higher the drones are, the less noise they make at ground level, and the less effective this ground-based microphone system will be. The drones have moved to elevations to make them more difficult to target with ground based weapons. Reductions in ground noise are a secondary effect.

The latest versions of Shahed can reach 5000m in altitude, which would largely be inaudible on the ground.

Wouldn’t a purpose built Esp32 with microphones aimed at the sky do a better job? It would be always on, better directional targeting.

There are extremely sensitive differential pressure sensors (like SDP600-25Pa) available from Sensirion that aren't overly expensive.

If these Shahed drones have a propeller they should have a brutal signature between 0-250Hz as they are moving a lot of air.

Use one differential side and connect it to a kitchen funnel for directional listening the other one to a plastic bottle with a tiny hole in it. This way the sensor "Null" out the environmental pressure (which the bottle follows very very slowly) from both inputs. It then only will pick up everything high frequency that's different to it.

This way I was able to detect washing machines that had a physical link to house walls for many hundred meters (machine spinning -> house wall shaking -> pressure waves) away.

Add this with some GPS PPS frame timestamping and you should have a nice tracking network that doesn't require a lot of bandwidth. But maybe the setup must switch to analog differential pressure sensors as these Senirion-I2C sensors do not have a Sync ping for super precise timestamping.

Baltics are very involved in the war in Ukraine, for instance, Slovenia started NAFO.