How far, small, and fast can meteors be detected?
$\begingroup$ I removed the 2nd question as answers to it will be unrelated. Detection is carried out by radar, lidar, optical telescopes etc from Earth and space. Evasion is an entirely separate question $\endgroup$– Rory Alsop ♦Apr 3, 2018 at 8:43
$\begingroup$ @Hobbes okay that's great! Nicely done too. $\endgroup$– uhohApr 3, 2018 at 9:06
Space debris is tracked via radar.
Asteroids are usually tracked via optical telescopes set up for that purpose. If they get really close to Earth, they may be tracked via the space debris systems too. In some cases, extra observations are arranged for asteroids that look like they may get close to Earth.
Meteoroids are too small to be tracked at long range. There are some efforts underway to record the trails they leave when entering the atmosphere.
$\begingroup$ Scott Manley's videos rock! I've asked a question about this one: Why did the distribution of asteroids discovered in 2010 have a radial modulation? $\endgroup$– uhohApr 3, 2018 at 9:30