I looked up this thread but could not find it, how do you set up specific aircraft registration alerts in the APP version of FR24 ?
Top left (the 3 horizontal lines) / Alerts / Custom Alerts. Then press the + sign (top right) and enter the reg (without any hyphens). And you can config whether you want the vibrate and/or the LED flashing.
This is Android – no idea what the IOS version looks like.
Very often, if when you get the alert you go to the app, the aircraft is gone and you see nothing. It may have been a very short flight, they may have turned the transponder on for only a short time, or they flew at a very low level.
I asked this Q above but I don’t think there is any way to see what triggered the alert, apart from the registration. The app won’t log the track. Maybe there are unofficial FR24 apps which log the track?
Ahhh OK, thanks, I will add it when Capital Controls in my country will be lifted and allow me to pay the 4,99 Euro to appstore for the specific feature 
The FR24 track for my most recent flight (EGKA-LJPZ) is here It can be played back.
It will be gone in a few days so I’ve saved the overall image:
One persistent thing about FR24 is that the ground speed is showing as too low by about 1.5×. I wonder how they work it out? If it was a triangulation issue it should average out.
Correct Peter, I watched your flight on FR24 and via the Autorouter flight tracker and the GS indicated by FR24 is off all the time.
It is a triangulation but it is inaccurate.
FR24 came up on this thread.
I don’t know if we discussed this before, but there seems to be a difference between what you see on the FR24 website and what you see on smartphone alerts. The alerts show much more than the website. But some testing would be needed to check this out.
Just checked out one particular aircraft. I got an alert on my phone (FR24 app) but the website says
This track shows where the triangulation fails to work:
Maybe this has been answered already, but I haven’t studied all of it. What I don’t understand is this triangulation. Triangulation either involves a known point and a direction, or a known point and an “amplitude” (distance from that point as used for mobile phones). With several of those, the position can be pinpointed. The FR24 receivers only receives some mode-s data? It cannot possibly determine direction? They are not directional devices. The only other possibility is distance, but how can it possibly determine distance when the “amplitude” is determined by loads of other factors (quality of receiver/transmitter, antennas, altitude and so on). ??
They receive a signal at a time. That allows triangulation.
