How to automatically determine if a given callsign is currently flying

I am interested in receiving a Boolean response to the question, “Is callsign N1234X being actively tracked?” What custom URL can I ping to get that answer? This is something I would like to have a webpage ping once in a while, then display TRUE with a flashing green light, and FALSE with nothing. Thank you in advance.

You would need to use the API to get that kind of data.

I will add alerts to the feature request list and some day we may be able to add it.