Still valid in 0.5.0.0.
The scanner is available only on interceptors, and must be activated manually from one of the radial menues. Note that it increases your ship signature, making it very easy to detect for the enemy team.
The spikes represent a station, base or an enemy ship.
Objects appear as a target labelled “Unknown” once close enough (around 10^2 km maybe).
The spike shifts to red and to the right when you move away from the target and shifts to green when you approach (proportionally from your relative velocity and maybe approach angle).
It can be very subtle:
Very green despite the low velocity. Might be due to the perfect angle (the signature I was hunting was already scanned and I was nowhere near its direction when I started to look around. The signature comes from the ships there I think)
There is no other directional information, so you must fly around to figure out in which direction a target might be (approach until distance starts to increase again, look around for an unknown object, try again in another direction).
Flying at high altitude give you more speed and therefore better relative speed indication. The last station I scanned was at 600km altitude.
There is a shortcut to change scanning frequency but it does nothing for me, you’ll have to figure it out.